Thesis Slag Desulphurisation

2009:065MASTER'S THESIS Improvement of the Desulphurisation Process by Slag Composition Control in the Ladle Furnace Stephen Famurewa Mayowa Luleå University of Technology Master Thesis, Continuation Courses Minerals and Metallurgical Engineering Department of Chemical Engineering and Geosciences Division of Process Metallurgy 2009:065 - ISSN: 1653-0187 - ISRN: LTU-PB-EX--09/065--SE IMPROVEMENT OF THE DESULPHURISATION PROCESS BY SLAG COMPOSITION CONTROL IN THE LADLE FURNACE Famurewa Mayowa Stephen Supervisors Professor Bo Björkman(LTU) Sven-Olof Ericsson(OVAKO) Luleå University of Technology Master Thesis in Minerals and Metallurgical Engineering Department of Chemical Engineering and Geosciences Division of Process Metallurgy ABSTRACT The cleanliness of steel with respect to non-metallic inclusions and the precise alloy compositions in the steel products have always been of great concern in steel making technology. The development of steel making process to meet the compositional requirements for specific mechanical properties such as ductility, toughness, fatigue and machinability requires dynamic and continuous investigations. The refining of molten steel in the ladle furnace to meet the required compositional range requires the optimisation of the process parameters. For sulphur removal control, parameters such as argon gas flow rate through the porous plugs, inductive stirring effect, vacuum pressure of the tank degasser, amount & composition of the top slag should be optimised. In this thesis project an investigation was carried out on the factors that influence the top slag composition before vacuum treatment and also to optimise the top slag composition for precise sulphur removal. 12 heats were followed during the project; slag samples, steel samples, temperature and oxygen activities were taken at eight different process stages at Ovako steel mill. A relatively large variation was observed for all the oxide components of the slag phase before vacuum treatment in all the heats followed. A PLS analysis made shows that topslag composition before degassing is influenced by the amount of slag former added, oxygen potential at tapping, the yield of Al and Si deoxidants into the steel at tapping. The model has a poor predictability because some important parameters such as ladle glaze condition, amount of EAF slag tapped and refractory wear could not be measured. An alternative solution of extra slag practice was suggested instead of modelling the composition and mass of carry over slag left after slag removal. The extra slag practice involves the addition of lime during tapping so as to aid the removal of all the slag before ladle refining and thus optimisation of the new synthetic slag for precise sulphur removal could be easily achieved. Finally the investigation of the desulphurisation process shows that degassing time, argon gas flow rate through the porous plugs are as well important as the slag mass and composition in order to achieve a precise sulphur removal. ii Robert Eriksson. Sven-Olof Ericsson for accepting me to carry out this research work under his supervision and also for sharing his rich experience with me during the course of the work. Hofors during my stay and all my friends in Luleå. who has granted me the scholarship to study in LTU. This could not have been. Patrik Undvall. This will be incomplete if i don’t appreciate my dearly beloved Abiola. I also appreciate the moral support of the members of Pingst Kyrkan. My profound gratitude goes to my supervisor at Ovako Steel AB. Rolf Nilsson and all the team members working at the EAF and Ladle furnace at Ovako Steel AB Hofors. My parents Mr and Mrs I.ACKNOWLEDGEMENT I am eternally grateful to my creator and my saviour whose mercy and love has been without limit in my life. without the support of my wonderful brothers. Famurewa Mayowa Stephen July 2009. B Famurewa you are part of what I am today. Sunday and Festus.I). who has been a good companion for me. I am grateful unto you all. I appreciate my supervisor in LTU Professor Bo Björkman for his contribution in this project work and his pedagogic style of knowledge transfer in the classroom. To him who gave this opportunity. Sölve Hagman. Lars-Erik Borgström. Ove Grelsson. I also like to appreciate the technical support of Jan-Eric Andersson. His mercy endures forever I want to appreciate Swedish institute (S. Hofors iii . .................1 Thermodynamic Theory .................................................. 18 2............................................................................................................................................................... 9 2...............3......0 LITERATUTRE REVIEW ............................................................................................................................................................................................................................. 18 2.............5 Temperature .........................................................2....... 1 1..............1 Electric Arc Furnace.................... 16 2.............................................................................................................TABLE OF CONTENTS ABSTRACT ..................................................2.............................................................................3...................... 6 2.................2 Refining Processes .......................3 Process Description at Ovako Steel AB Hofors .................................. 19 iv ......1.......... 6 2......................................................................2..2 Alloying....................................................1.............. iv 1.............................................................3 Kinetic Theory.......................................................................................2 Slag Properties................4 Sulphur Distribution Ratio ..................... 12 2................................................ ii ACKNOWLEDGEMENT ......... 15 2...............................1 General Steelmaking .................................................... 2 1...............4 Effects of Sulphur on Steel............................1 Background ............................................2.......................2 Ladle Furnace Refining .....5 Aim of the Project ................................. 1 1.................................................................................................................. 8 2................2............................................... 9 2................2....3................................................................................................................................................................... 4 1........3....3 Stirring...................................2 Sulphide capacity .............................................................2......... 9 2.3...........................................................0 INTRODUCTION ....2 Historical Background of Ovako....................1 Composition .......... 8 2.................................................. 3 1............................................................ 17 2.......................3.....................................1 Deoxidation .................................. 7 2..............................3..... 8 2.........3 Oxides Activities .................... 6 2.3 Desulphurisation....3.............................................................................3................................................................................................. 4 2.....2.................................................................1 Argon Gas flow rate ...............................................................................................3. 12 2............................................................... iii TABLE OF CONTENTS .......... ....................................................................................................................2 Viscosity ............................................................ 41 4..............................................................................1 Experimental Procedure ..................0 RESULTS AND DISCUSSIONS .......... 27 4....................................................2 Method ............................................................................................. 27 4..6 Equilibrium sulphur Distribution ............................................................................................................. 47 REFERENCES ............................................... 21 2..................................... 34 4................. 46 5................... 43 4.1 Conclusion..................................................8 Equilibrium Condition during Vacuum Treatment ...................4 Dilution Slag ......... 23 3.................................................................................9 Equilibrium Sulphur Content in the Bulk steel .......................3............................ 36 4.................10 Optimisation of the top slag composition ................................ 23 3.... 38 4......0 MATERIAL AND METHOD ............... 21 3............................ 30 4.............................................. 25 4.................................................................................................................. 27 4............................................. 46 5.............5 Oxygen Activities ....................2Analysis Procedures and Techniques: ...................................................4 Regression Analysis for the Top Slag Variation .........................2....................... 50 v ......................................................................................................................... 23 3......................................................................................1 Synthetic Slag Composition ............................................. 44 5........................2 Top slag compositional changes ......0 CONCLUSION AND RECOMMENDATIONS ............ 48 APPENDICES .............................................................................................................................3.........................7 Regression Analysis for the Desulphurisation Process ...............................1 Material ....................................................................................................................2 Recommendations ................................................................3 Mass Balance................................................ 23 3................................................................................... 31 4.............2....2............... Figure 1 shows the production of steel in the world in 2008. Figure 1: World Steel production (2) 1 . Its world productions in million metric tons are 1251.1.2 in 2008 (2). crystal arrangements. this also proves its wide versatility in material consumption.0 INTRODUCTION 1.2 and 6 million metric tons in the past 6 years with minimum of 5. The world production of crude steel as reported by world steel association is to a great extent more than any other metal product.1 Background Steel and its products are undoubtedly the pillar and anchor of material developments through the ages. 1251 and 1329 in the year 2006. There was a decrease in the crude steel produced in the world as well as in Europe and Sweden in 2008 compared to 2007. The production of steel in Sweden has been between 5. 2007 and 2008 respectively (2). chemical compositions and several other material properties leads to its wide areas of present use and continuous possibility of future developments(1). It is the base material for over 2500 different grades of products (1) . The potential ability to modify its structures. It is a substantial part of material science and a key material in product development in modern technological advancement. Italy. automotive and engineering industries. France and Netherlands with several sales companies in Europe and the USA with a total annual production of about 2million tones of steel of "right quality" (3). Steel products could also be classified into three based on the composition of alloy additives. It has 15 production sites in Sweden Finland. The primary operation areas include. Wire. Bright Bar and Tube&Ring. Steel from iron ore (hematite or magnetite) are mainly produced in integrated steel mills while steel from scrap based materials are produced in EAF operated mills.The production of steel could be classified into two. Ovako Steel. low alloy steel. 1. tubes and rings. Present day Ovako was established in 2005 by a merger of 3 re-known steel companies. the new company decided to continue its operation in a specific steel product (3).2 Historical Background of Ovako Ovako is a leading European long special steel producer whose production covers low alloy steels and carbon steels in the form of bar. Ovako consists of four product divisions namely. Due to strategic and technical reasons. medium alloy and high alloy steel (1). heavy vehicle. Bar. Fundia Steel and Imatra Steel. rod. based on the raw materials. Figure 2: The Group Structure of Ovako showing the products and their production sites (3) 2 . The origin of Ovako could be traced to strong Nordic steel production technology and the forerunners to the company were founded for over 300 years ago. ore based and scrap based raw materials. wire. Figure 2 below shows the four product divisions with their respective production sites. Sampling is carried out during the melting to check the temperature in the furnace and also elemental compositional of the molten scrap. The ladle is transported further by crane to the ASEA-SKF unit and the ladle glaze from the previous heat. The ladle proceeds to the vacuum degassing where desulpurisation is done as well as gas and inclusion removal. Also slag formers are added. EAF slag and part of deoxidation products (Al2O3 and SiO2) which have floated to the top of the steel and other impurities are removed at the mechanical deslagging process.9ton of slag former (lime) addition. Alloying is done through lumpy alloys and wire feeder. tap hole sand.3 Process Description at Ovako Steel AB Hofors At Ovako Steel two scrap baskets with a total weight of about 110ton are charged into the oval bottom tapped (OBT) electric arc furnace (EAF). The steel is tapped into the ladle where it is deoxidized with aluminum and silicon (FeSi). The steel in the ladle is then transported further in a ladle wagon to the heating unit where it is heated using electric energy through three graphite electrodes. The second scrap charge into the furnace is followed by the addition of 1. A schematic description of the entire steel making process at Ovako Steel AB is shown in Figure 3. The electrical melting with graphite electrode and combustion from the oxy-fuel burners proceed after the first scrap charge with 1. Slag Removal Melting Scrap Charging Ladle Furnace Vacuum Ingot To Rolling Mill Stripping Ingot Teeming Figure 3: Steel making Process at Ovako Steel AB 3 . The desired phosphorous refining and heat condition is achieved after about 48 minutes of power-on. Dust and off gas produced during the melt down are collected by off gas evacuation system. Sample of the steel is taken after tapping and deoxidation in advance for further refining.1.6ton slag former (lime or dolomite) and then by carbon and oxygen injection for slag foaming. The ingots are stripped and then transported to the pit furnaces for heat treatment prior to rolling or forging. 1. This success led to the increase in the effect of sulphur in the steel.5) 1.The steel temperature is finally adjusted to casting temperature and the composition is checked to be in agreement with the aimed composition. (4. for example ball bearing steel grades.2ton weight using up-hill teeming. these effects become somewhat more intense than earlier noticed (4). and etc. a successful result achieved was a further reduction from about 20ppm to 5ppm. crack initiation point) (4) . i. Formation of undesirable sulphides which promotes granular weaknesses and cracks in steel during solidification. tube and ring. In some other steel products sulphur content is refined to its minimum due to its negative effect on the mechanical properties. The final products after processing in the rolling mill and tube& ring mill are in the form of bar.4 Effects of Sulphur on Steel Sulphur has a positive effect on steel when good machinability is desired of the steel product. ii. The production of steel grades used for the manufacturing of ball bearing requires very low oxygen content in other to reduce the possibility of formation of non metallic oxide inclusions such as Al2O3. The present state of production in Ovako at the commencement of this project was able to meet 4 . The following effects of sulphur become more significant when the oxygen content is successfully reduced. which have deleterious effect on the final products (fatigue life. The 100ton refined molten steel is finally teemed into 24 ingots each of 4. It lowers the melting point and intergranular strength and cohesion of steel iii. Sulphur contributes to the brittleness of steel and when it exists in sulphide phase it acts as stress raiser in steel products.5 Aim of the Project The above mentioned effects of sulphur are highly undesirable in the production of some special steel products. A lot of research work has been done on the reduction of total oxygen content of steel. since the operating condition of such steel grades requires high fatigue strength and other similar mechanical properties. However the focus of this project work is to improve the desulphurisation process during vacuum degassing at the ladle furnace. The compositional variation of the slag formed after deoxidation was studied with respect to the dissolved oxygen content of the steel at tapping. Optimum synthetic top slag practice with improved sulphide capacity. by slag composition control. 5 . steel compositions. temperature and some other factors were analysed for their sulphur removal potential using some empirical models and later compared with actual measurements in the plants. for accurate desulphurization for different steel grades was to be estimated and the effects of the different kinetic parameters were to be investigated. This involves an extensive study of the thermodynamics of the process and kinetics. It is focussed on increasing the level of accuracy of the process to meet the desired sulphur content of the steel product and also to shorten the degassing period.the low sulphur requirement ranges of the different steel grades but with a low level of accuracy. Slag properties (especially composition). These involve extra sulphur addition when the sulphur removal is too high or further refining when the removal is too low. The ladle refining of different steel grades and different slag practice were followed daily. The mass of slag remaining after deslagging and its influence on the final slag composition were also investigated. Metallurgically. All the mentioned scrap types are used in Ovako steel production process.1 Electric Arc Furnace The Electric Arc Furnace is a Steel making technology which is employed for about twentyfive percent of the world steel production (5). Slag Foaming This is a common praxis in the EAF. equipped with spout also exist). preheating the scrap is beneficial. It also decreases the hydrogen contents in the steel as dry charge are fed into the furnace but the extent of preheating is limited to avoid evolution of undesired dioxin. External high current electric arc heating with a better thermal control than the basic oxygen Process is used to melt steel scrap and converts it into liquid steel.1 General Steelmaking 2.0 LITERATUTRE REVIEW 2. Another important function of this praxis is to cause a foaming of the slag provided 6 . Fluxing agents (lime and dolomite) are added as slag formers to remove impurities. made of heavy steel plates with a dish-shaped refractory hearth and three vertical graphite electrodes extending downward from a domeshaped removable roof. Oxygen and carbon are also injected into the furnace for slag foaming. sampling (composition and temperature) and tapping. Carbon or coke is injected into the furnace to increase the melt down efficiency by supplying additional energy from combustion with injected oxygen and also to cause carbon boil which promotes stirring to achieve a good slag/metal mixing. The furnace is mainly eccentric bottom tapped vessel (though oval bottom tapped vessel. refining.2. and the choice depends on type of steel products (1). The furnace is also often equipped with oxy fuel burners for energy efficiency reason. process scrap (scraps from the manufacturing of steel products) or obsolete (scraps from the end of life of used equipments). The furnace could be tilted backward for slag removal and forward for about 10-18º for tapping. melting down. charging of scrap (direct reduced iron is included in some charges). The cycle of operation for the production of steel in the EAF involves. The scarp charged into the furnace could be home scrap (scraps within the steel mill). as it reduces the energy requirement for melting the scrap which further reduces tap to tap time and the overall productivity.1. 1. Alloying iii. The oxygen content of molten steel is often extrapolated using the carbon content in an online production process. 7 . Degassing to remove hydrogen. deslagging. Adjustment of temperature to optimum range before casting (7). Desulphurisation v. stirring with gas or electromagnetic fields and vacuum treatment (5.0025 X CO pressure---------------------------------------. nitrogen and other gaseous inclusions vi. Electrical heating. chromium and iron are also oxidized. Deoxidation ii.2 Ladle Furnace Refining The secondary stage of steelmaking process is done in an open topped cylindrical container lined with refractory called ladle. 7). i. The units of operation mentioned above enables the following refining and adjustment operations. Stirring to achieve temperature and composition homogeneity and improved refining iv. The slag foam decreases the energy loss. In theory dissolved oxygen and carbon content of steel will react to form carbon monoxide until equilibrium is reached C + O = CO(g) ∆Gº = -18319 .369T -------------------------(1) % C X % O = 0.(2) Reaction 1 will reach equilibrium when the relationship in equation 2 is attained (5). The primary step is done either in the converter or EAF and crude steel is produced (7) . decreases refractory wear and protect the water cold panel at the top of the vessel (1. silicon. wire feeding. especially phosphorous removal although manganese. The injection of oxygen performs some refining operation in the EAF. The unit metallurgical processes in the ladle include.the viscosity of the slag is not too low. Removal and modification of inclusion vii. 7).41. 2. slag foaming. 8 .7) . The addition of alloying elements results into temperature drop of the molten steel and the calculation to meet the final composition is often done by computer programmes. The rate of heat loss is reduced in most ladle operation by preheating the ladle before tapping.2 Refining Processes 2. as oxygen is injected into the EAF for refining. 2Al + 3O = Al2O3(slag) ∆Gº = -1205115+386. and the oxides nucleate to diffuse to the ladle wall or absorbed into EAF slag. Final steel products require a very low content of oxygen and also further refining and alloying are most desirable at the minimum oxygen content. and other process control measures.1 Deoxidation The oxygen content of the steel tapped into the ladle after melting in the EAF is often high. The addition of strong deoxidizers such as aluminum and ferrosilicon is done during tapping.2.(4) The deoxidation reactions shown in equations (3) and (4) are exothermic and thus the temperature of the liquid steel is increased. Most of the alloying elements are lumpy ferroalloy since they are cheaper to produce and available in different grades to suit the final steel compositional requirements.8) . heating of ladle lining and by flux through the lining and shell (5). they could either be placed in the preheated ladle before tapping or run into the tapping stream so as to utilize the mixing effect of the tapping stream to achieve thorough deoxidation (5.2.655T ------------------------------------. 2. A wire feeder runs wire of alloying elements at controlled speed into the steel (5.2.2 Alloying The adjustment of the final composition of the molten metal is done at the heating and wire feeding position of ladle station. for this reasons there is a need to kill or deoxidize the crude molten steel.714T ------------------------------------(3) Si + 2O = SiO2 (slag) ∆Gº = -580541+220. however the steel also loses heat by radiation from the top surface. The reaction is shown in equation (3) and (4). These two stirring means are important for good metal/slag interaction to achieve an effective ladle refining. 2. desulphurisation becomes an important subject to be continuously investigated for highly clean products which can withstand market competition and satisfy customer's demand.3 Desulphurisation Desulphurisation is an essential practice in the production of clean steel products such as bearing steels with high fatigue strength which function under high impact operational requirement. 9 . however it is mainly carried out in a reducing conditions when the oxygen activity is low(8). It also aids continuous slag metal reaction with the aim of sulphur. metal and gas interactions in the ladle refining with consideration to sulphur removal.2. nitrogen and inclusion removal (6). desulphurisation is done during the vacuum degassing in the ladle furnace using lime saturated multicomponent slag. Ovako Steel AB specializes in the production of bearing steel products. At Ovako Steel AB. electromagnetic accessory for inductive stirring and permeable refractory block at the bottom of the ladle called porous plugs for gas stirring.1 Thermodynamic Theory When studying the thermodynamics of slag. the main parameters are discussed later in the report while the theories related to this project work are explained below. 2. ladle furnace technology is equipped with either one or both of the two stirring facilities. desulphurisation could be done at different points in the steelmaking process and with different reagents. [S ] + (O 2− ) = [O] + (S 2− ) ( ) − − − − − − − − − − − − − − − − − − − − − − − − − − − − − (5) ( ) 1 2 S ( g ) + O 2− = 1 2 O( g ) + S 2− − − − − − − − − − − − − − − − − − − − − − − − − − (6) [S ] + 1 2 O( g ) + = [O] + 1 2 S( g ) − − − − − − − − − − − − − − − − − − − − − − − − − (7) The equilibrium constant for the reaction in equation (6) is expressed as. Based on the production route and the type of steel product. hydrogen.3.2.3 Stirring Generally. It enhances homogenous temperature and composition of the steel. the reactions below are important. The parameters which influence the desulphurisation process are either thermodynamic or kinetic parameters. 8.are the activities of sulphide and oxide in the slag. 8. 9)..and aO2.. − − − −(11) where OpticalBasicity Λ = ∑ X 1n1 + X 2 n2 + X 3 n3 + ..913 + 42... aS2... sulphide capacity is often expressed in terms of temperature and composition as process control tool (5.  22690 − 54640Λ  Log C S =   + 43...84 Λ − 23.. Since oxides activities and the partial pressure of gaseous phases are not readily available as process parameters..6Λ + 25.. X is the mole fraction of the oxides in the slag system. Young et al showed that equation (11) only applied to range where Λ = 0.. K6 is the equilibrium constant for gas-slag reaction in equation (6) (4. n is the number of oxygen atom in a molecule of each oxide and Λth represents the optical basicity of each oxide (14). 13')..2 − − − − − − − − − − − − − − − − − (10) T  ∑ X 1n1Λ th1 + X 2 n2 Λ th 2 + X 3n3Λ th3 + .2223(% SiO2 ) − (% Al 2 O3 ) − − − (12) 10 .. 14).. and therefore reported correlations for ranges with Λ < 0.K6 = K6 = aS 2− aO 2 − ⋅ PO 2 PS 2 f S 2 − ⋅ (% S )slag aO 2 − ⋅ PO 2 PS 2 − − − − − − − − − − − − − − − − − − − − − −(8) Also sulphide capacity can be written as Cs = K 6 ⋅ aO 2 − f S 2− C S = (% S )slag ⋅ − − − − − − − − − − − − − − − − − − − − − − − − − − − − − (9) PO 2 PS 2 Where [S] and [O] are dissolved sulphur and oxygen in the steel respectively while (S2-) and (O2-) are sulphide and oxide (with free oxygen ion) in the slag respectively.8.. Log C s = − 13. Sosinky and Sommerville derived an expression to correlate optical basicity with sulphide capacity at temperature range between 1400 andd 1700˚C (4..82 Λ2 − 11710T −1 − 0. Also the expression is suggested for CaO. if alumina inclusion is considered in the equilibrium. K17 is the equilibrium constant for the deoxidation reaction shown in equation (15) (4. is the interaction parameter between sulphur and other elements j in the steel. Log K 7 = LS = = aO (% S ) ⋅ [% S ] f S ⋅ C S − 935 + 1.375 T (%S ) [% S ] Log LS = − 935 + 1. 15). The activity of oxygen in the steel could be calculated assuming equilibrium between the dissolved oxygen and aluminum in the steel and alumina in the slag or alumina inclusion in the steel bulk.275(%CaO ) + 0.387T ( KJ / mol ) − − − − − − − −(15) a Al2O3  − ∆G  K15 = exp = 2  RT  a Al aO [ ][ ] 3 Where aAl2O3 is the activity of alumina in the slag or as inclusion. aAl2O3 is taken to be 1.167(%MgO )] + 0. a Al = f Al ⋅ [% Al ] Log a Al2O3 = − − − − − − − − − − − − − − − − − − − − − − − − − −(16) [− 0. Wagner's expression can be used Log f S = ∑ eij ⋅ [% i ] .375 + Log C S + Log f T S − Log aO − − − − − − − (13) To calculate the activity coefficient of sulphur in the metal. Al + 3O = Al2O3 ∆G° = −1205 + 0. − − − − − − − − − − − − − − − −(14) aO and aS are the activities of oxygen and sulphur in the molten steel respectively. and aO and aAl are the activities of oxygen and aluminum respectively.560 − − − −(17) 2 % SiO2 3 The oxide composition is in weight percent and the expression has been proven to be valid for temperature ranges close to 1600ºC (4) . eSj .10- 11 . K7 is the equilibrium constant for the gas-metal reaction in equation (7).033(% Al O ) − 1.Andersson et al (4) studied the distribution of sulphur and the extent of sulphur removal using equation (7) K7 = aO aS PS2 ⋅ PO2 Also. The activity of Al can be calculated using equations (14) and (16) while the alumina activity can be calculated using Ohto and and Suito empirical expression in equation (17). liquidus line 'ab' represents a perfect unity of CaO activity. The ability to extensively describe the thermodynamic and thermophysical properties of the notable phases as a function of the composition and temperature of the slag is a strong control tool for desulphurisation (16) .60wt%.0-50wt% and MgO: 0-30wt% which is a fairly good range for the slag studied in this project work 2.SiO2. one of the important conditions to enhance the reaction is the activity of CaO. For the system considered in Figure 4. An optimum slag composition should be saturated with CaO. The ternary phase diagrams of CaO-SiO2-Al2O3 can be used to establish the optimum slag composition at a particular temperature.1 Composition The different phases in a multi-component slag system play significant roles in ladle refining with focus on desulphurisation. Al2O3. CaO + [S] = CaS + [O] -----------------------------------------------. Any composition within the homogeneous liquid region with an activity of CaO close to unity is good for desulphurisation process. in other words the activity of CaO in the slag should be close to unity to facilitate the exchange of the dissolved sulphur in steel with oxygen ion (6. while the remaining sections show undesired solid regions.2 Slag Properties The process of desulphurisation depends to a great extent on the properties of the slag phase.2. 2.18).(18) The general equation for desulphurisation is written in equation (18) above. Figure 2 shows an isothermal section of CaO-SiO2-Al2O3 slag system.3. 12 . the highlighted portion shows the homogeneous liquid region at temperature 1600ºC.3. 10-50wt%. It has also been established that high amount of slag is favourable for sulphur removal (17). CA6=CaO⋅6Al2O3. It should be noted that composition affects viscosity of the slag.5 with the relations 2AlO1.1600ºC Figure 4: Isothermal section of the phase diagram of the system. 6 and 7 show the activities of CaO.5)2 = aAl2O3 at 1600° C. CA=CaO⋅Al2O3. (18) Figure 5. C3S=3CaO⋅SiO2. CA2=CaO⋅2Al2O3. CaO-SiO2-Al2O3 at 1600°C. thus the kinetic will be negatively influenced (6). An optimum slag composition for good desulphurisation can be carefully chosen by exploring these diagrams to have the highest possibilities of CaO activity. Figure 5: Activities of CaO in CaO-SiO2-Al2O3 multicomponent system. The shaded area indicates the anticipated homogeneous liquid region at 1600°C. A3S2=3Al2O3⋅SiO2. SiO2 and Al2O3 respectively at different points in the homogeneous liquid region of the slag system at the 1600C. C2S=2CaO⋅SiO2. if the CaO of the multicomponent slag system is higher than 60% it has a negative effect on the sulphide capacity of the slag as it becomes heterogeneous and more viscous. (14) 13 .5= Al2O3 and (aAlO1. Standard State of pure AlO1. basicity and efficient fluidity. 5 with the relations 2AlO1.5= Al2O3 and (aAlO1. Standard State of pure AlO1. (14) 14 .Figure 6: Activities of SiO2 in CaO-SiO2-Al2O3 multicomponent system at 1600°C (14) Figure 7: Activities of Al2O3 in CaO-SiO2-Al2O3 multicomponent system .5)2 = aAl2O3 at 1600°C). Its ability to compare the desulphurization characteristics of different slags has led to the creation of several models for its measurement (6. 10.2. Compositions close to line ab also have CaO activity close to unity and high basicity which are important for desulphurisation (14).2. It is the potential ability of a completely homogeneous molten slag to remove sulphur during slag metal interaction (4. 16. For an optimal slag composition aimed to achieve an effective desulphurisation. 19). CaO-SiO2-Al2O3 at 1650°C showing the Log of Sulphide capacity with composition in mass % (14) 15 . 17. 14) . a b Figure 8: Isothermal section of the system. This potential ability is used to estimate the amount of sulphur that a slag of a given composition will retain under a specified condition of oxygen and sulphur pressures (19) .3.2 Sulphide capacity An important property of slags which plays a vital role in the investigation and control of desulphurization process is sulphide capacity. Figure 8 shows the sulphide capacities of a CaO-Al2O3-SiO2 system at different compositions. It is often used to establish the sulphur distribution ratio between slag and metal at equilibrium. compositions close to line ab (-Log Cs = 1) should be ensured. 3 Oxides Activities The activities of oxides in the molten slag and alloying elements in the molten metal as well as the temperature of the process determine the equilibrium oxygen potential in the system. a measure of the electron donor power of slag will be used in the estimation of the sulphide capacity.2. it is known that desulphurization is improved with slags of higher basicity. Figure 9: Sulphide Capacity values as functions of Basicity (4) In this project work optical basicity. Oxides activities in the slag affect the equilibrium activity of oxygen in the steel and also the basicity of the slag.3. 2. Figure 9 shows three different sulphide capacity models. the activity of alumina is low and the oxygen activity will also be low provided the Al content of the steel is high at this condition. The measurements of the activities of oxides in the slag and dissolved oxygen in the steel are important for control of desulphurization process (10) . Significant correlations have been made between sulphide capacity and basicity.Basicity is defined in its simplest form as the ratio of %CaO / %SiO2. This is a necessary requirement 16 . The three models in figure 9 show that sulphide capacity is improved with increased basicity. Basic slags have high content of basic oxides which are network breakers with ability to release its oxygen ion (O2-) in exchange for the dissolved sulphur in steel. Figure 10 shows that at high basicity. Sosinky & Sommerville. Young et al and KTH models. The first two models were calculated from optical basicity while the third is a model developed in the division of process Metallurgy in KTH (4). because its model have been proven to have a fair agreement with empirical data and the parameters can be accessed. 3. oxygen activity and sulphur content of the molten steel (16). Isothermal section of the system.2. A good estimation of this parameter indicates a good control of the process. due to its equilibrium with Al and Si content of the steel.Al2O3-MgO with 5%MgO at 1600°C showing the sulphur distribution between Metal and Slag at equilibrium (14) 17 .for desulphurization. It is a function of temperature. An optimized slag which can be used to control desulphurisation can be obtained by exploring the ternary diagram shown in figure 11 Figure 11. CaO. 2. sulphide capacity of the slag.SiO2. (20). Figure 10: Alumina activities for typical ladle furnace slag using the KTH model and Ohta and Suito Equation (16).4 Sulphur Distribution Ratio It is an estimation of the sulphur reduction in a desulphurization process. It is the ratio of the sulphur content in the slag and metal phase at the end of vacuum treatment. Also Turkdogan E. established that low SiO2 content of the slag is favorable for improved sulphur removal. 2.3.2.5 Temperature An essential parameter in desulphurization is the temperature at which the process is carried out. It influences the viscosity (favourable kinetic condition) and sulphide capacity of the slag and also sulphur distribution in the metal and slag. Most models that have been developed to evaluate the sulphide capacity of slag were mainly functions of temperature and composition (10,11,12,17) . Figure 12 shows that sulphide capacity is improved at higher temperature. The calculation was done at constant MgO and SiO2 contents of the slag and also at constant %Al and %C content of the steel(11). It is also reported that desulphurisation is slower at the later period of vacuum degassing due to reduced sulphur content of the steel and temperature drop during the process which is unfavorable for the sulphide capacity (4). Figure 12: Sulphide capacity as a function of temperature and Al2O3 in the topslag(11). 2.3.3 Kinetic Theory The transfer of sulphur atoms from the metal phase to the slag phase and the transfer of oxygen ions from the slag phase to the metal phase during sulphur refining process is controlled by mass transfer through diffusion (12, 19) . Fick’s law of diffusion could be applied to the process as below, 18 J = −D ∂Φ ∂x [% S m ] − [%Si ] V∂[% S ] = −D δ A ⋅ ∂t ∂[% S ] − K t ρ m A = [% S m ] − [% Se ]− − − − − − − − − − − − − − − − − −(19) ∂t M Where J- Diffusion flux D- Diffusion constant ∂Φ - Concentration gradient ∂x [% S m ]− Initial Concentration of Sulphur in the melt %wt [% Se ]- Concentration of Sulphur in the slag/Metal interface at equilibrium %wt δ - Boundary Layer Kt- Total mass transfer coefficient M- Mass of steel A - Slag-Metal interface area V- Volume of steel ρ m - Density of steel ∂[% S ] - Sulphur removal rate and [%S] is the instantaneous sulphur concentration in steel ∂t As earlier mentioned sulphur removal depends on the stirring rate and viscosity, both properties affect the slag metal interface area and also mass transfer coefficients of the process. It should be noted that these constant δ and Kt are difficult to measure in a real process and the modeled values are specific for particular stirring conditions (12) . The conventional assumption of a flat and horizontal slag metal interface area 'A' has been proven to be an under estimation as the slag is dispersed in the steel and the interaction area is more than supposed (12). 2.3.3.1 Argon Gas flow rate The manipulation of the inductive and gas stirring during the Ladle refining is a very important factor in the desulphurization process control. An investigation of the influence of argon gas flow rate on desulphurization during vacuum treatment is shown in Figure 13. With respect to desulphurization, the optimum condition for vacuum treatment in the figure is at the argon gas flow rate of 1.8m3Ar/min, thus a better desulphurisation is achieved optimum slag/metal mixing (6). 19 Figure 13: Steel Desulphurisation during Vacuum treatment at various Ar stirring rates (13) The position of the inductive stirrer and the rate of flow of argon gas through the porous plugs were studied by Hallberg et al (17) in the creation of a process model for sulphur refining at Ovako Steel AB. It could be deduced from figure 14 that argon gas flow rate through the porous plug has an influence on the fluid flow in the ladle, a low flow rate at the first porous plug which is closer to the inductive stirrer and high flow rate at the second porous plug which is at the opposite side is necessary for a good desulphurisation (17). Figure 14: Influence of different argon gas flow rates on sulphur removal for combined gas and inductive stirring (17) 20 using computational fluid flow dynamic predictions. A low melting point CaO rich slag can be synthesized by adding a correct proportion of Al2O3.2 Viscosity It is a thermo-physical property that influences the kinetics of the ladle metallurgy (16) . Another trial with inductive stirring and calm argon gas stirring at the final heating unit process after the vacuum treatment shows no influence on the final sulphur content of the steel though it had a positive impact on inclusion removal (6). It should be noted that the flow rates through the porous plugs are not fixed throughout a heat at Ovako Steel AB.Most of the top slag is concentrated above the second porous slag where they are hit by the gas plumes from the plug and thus a greater contact area between slag and steel is created.4 Dilution Slag A major quest in this research is to identify the source. This is substantiated by the authors.13). The control of argon gas flow rate was difficult at the heating station of ladle due to poor flow of gas through the porous plug. 2. (6. they are rather extrapolation of temperature and composition in a multicomponent slag system (16). This poses a problem to the optimization of the slag mass and composition for a precise sulphur 21 . Viscosity values for steels are reasonably well established at steel making conditions but the viscosity of slags are not. composition and mass of the slag which remains after mechanical slag removal in steel making process line at Ovako. The viscosity of both the steel and slag affects the mass transfer during the ladle refining. they are changed by the operators based on reactions observed in the camera view. and the viscosity is adjusted in some steel plants by the addition of CaF2. mass transfer rate of sulphur is improved due to easy dispersion in the steel and the slag/metal interfacial area is increased (13) .3.3. Some previous projects done at Ovako Steel AB have also investigated the effects of argon gas stirring before and after vacuum treatment on desulphurisation (6). At low viscosity of the slag. The only trial that was done was unsuccessful with a poor sulphur removal and poor vacuum treatment. 2. 22 . The condition. this particles hang on the wall of the ladle as glaze and are flushed off when liquid steel is poured into the Ladle during subsequent heat. It will investigate the slag mass and composition during different process stages and attempt to optimize the slag with the aim of controlling sulphur refining process. The reaction products. 2. this project work will advance sulphur removal process at Ovako steel AB Hofors using slag composition control. EAF Slag: Hot heel is a common praxis at Ovako steel. as the hole is opened before steel falls into the ladle. 1. is reduced by the addition of aluminium metal and Ferrosilicon alloy. With consideration to all the theories of sulphur removal as well as thermodynamic and kinetic properties discussed earlier. The oxygen contents which is often between 100 and 1000ppm before tapping depending on the extent of refining and the heat condition in the EAF. thereby forming non metallic particles after reacting with refractory. Al2O3 and SiO2 indigenous inclusions are major sources of inclusion in steel making and as well increase the amount of the EAF slag as they are absorbed after nucleation and separation from the steel bulk. Deoxidation Products: To enhance further refining after melting of scrap in the EAF. Despite the hot heel practice. about 110tons of steel scrap is charged into the EAF and less than 105tons is tapped into the Ladle leaving some steel behind in the furnace. The tap hole sand is rich in MgO and SiO2 and its quantity in the tapped stream depends on the age of the tap hole. the tap hole is blinded with Olivine sand. composition and the amount of the glaze depends on the steel type produced at a particular heat. As teeming proceeds the temperature of the system drops and fluidity of the slag reduces. 3. A preliminary study of the process shows the following possible sources of the dilution slag. Ladle glaze: Ladle glaze is formed when draining the Ladle into the mould.removal. 4. reduction of oxygen contents of the steel is important. as top slag comes in contact with refractory (21). Tap hole sand: After each tapping. it is unavoidable to have a small mass of slag entrained in the tapped steel. this also considered as a probable source of dilution slag during ladle refining. It is of course certain that this sand will be lost into the steel during tapping. 02 S 0. including home.80 12.679 3. coal. mass of additives and also consideration was taken of the vacuum pressure and argon gas flow rate at degassing.30 17.065 0.78 91. oxygen.017 0.45 FeO 0. The selection of the scrap materials is based on the size and grade of the scrap and also on the cleanliness or type of the steel to be produced.006 TiO2 0. dolomite Alumina and pure Alumina). slag composition. process and obsolete scraps. right from melt down in the EAF to the end of casting. The additives used in the process includes anthracite.22 Pure Alumina Measurement is in wt-% MnO 0. oxygen activity.90 MgO 0. The aim was to observe the consequential effects on desulphurisation. The chemical composition of the slag formers used at the ladle furnace refining is given in table 1. steel composition.198 0.58 4. deoxidants (Aluminium metal and Ferrosilicon) and other alloys. The studied parameters include temperature.3.2. slag formers (Lime.91 2.13 0.1 Experimental Procedure A number of heats were followed to observe the compositional changes in the steel and slag at different process stages. 23 .08 0.1 Material The raw materials used at Ovako Steel AB are steel scraps of different grades.2 Method 3.0 MATERIAL AND METHOD 3.22 Al2O3 0.020 CaO 92. Table 1: Chemical Composition of slag formers Lime Alumina SiO2 2.050 0.78 2.17 0. Different steel grades were followed to investigate the variation in the studied parameter.93 63.430 0. O4. Figure 15: Sampling points for plant trials B . O6. Slag sample. T7: Steel sample. 3. T . S1. T1: Steel sample. Oxygen activity and Temperature at arrival at the ASEASKF Ladle furnace station before alloying 5. S .Temperature 1.Oxygen activity. S2 : Steel sample and Slag sample at the end of tapping.Bulk steel sample. S5. 7. B6. Slag sample.Eight sampling points were observed at different subunits in the integrated process line for thorough follow up of the equilibrium conditions and changes in the system. Slag sample. T6: Steel sample. Oxygen activity and Temperature before degassing 6. B8 : Steel sample during casting. 8. B4. T4 : Steel sample. B1. Slag sample. S3: Slag sample before slag removal 4. Oxygen activity and Temperature after degassing. The schematic diagram of the sampling points is shown in Figure 15. O1. O . S7. T5 : Steel sample. B2. O5.Slag Sample. Oxygen activity and Temperature in the EAF just before tapping respectively 2. B7. 24 . B5. S6. Oxygen activity and Temperature after extra alloying (if there is any). O7. Cr2O3 and other oxides in minor concentration were measured.2Analysis Procedures and Techniques: Temperature: The temperature of the molten steel was measured in the EAF with the aid of Robot and at the Ladle furnace using the automatic sampling lance. Mo. Mn. SiO2. Ti. they were ground into powder in a ring mill. MgO.2. V. Cr. Chemical Composition of Slag Samples: The slag samples were taken at each designated process stage using the slag spoon. sieved to collect fine particles less than 10µm which are void of metallic iron. Al2O3. the samples were saved for further analysis. In some occasions for the purpose of this thesis work the temperature was measured using the electro nite Celox R7 oxygen activity measuring equipment. Mg and other minor elements.3. Sulphur and carbon in the samples were analysed with LECO CS-444 using the melting and combustion method. the samples were sent to the operation laboratory were immediate analysis was made. This analysis was done in LECO-CS 200 equipment using the melting and combustion method. TiO2. Ca. ARL OES 4460) for the concentrations of Al. Si. P. MnO. The prepared samples were then heated in a laboratory furnace for about 8 minutes before they were arranged in the PAN analytical Axios equipment to analyse the oxide composition using the wavelength dispersive X-ray fluorescence technique. similar to the temperature lances said earlier were used to take steel samples at each point mentioned above. The samples were prepared before analysis. The relative analysis accuracy of these elements depends on their concentrations. The samples were analysed by optical emission spectroscopy (Bausch & Lomb. Chemical reagents were added according to standard and then thoroughly mixed together. 25 . The concentration in weight percent of CaO. A portion of the samples taken after grinding to fine size was also analysed for sulphur and carbon content. Chemical Composition Steel Samples: Automatic lances. the value of which is displayed on the screen of the equipment. In the project work the activity of oxygen in the steel melt was measured using the Celox sensor designed by Heraeus Electro-Nite. The sensor contains ZrO2 elctrolyte with a molybdenum wire in Cr/Cr2O3 as a reference electrode while the bulk steel is the second electrode.Oxygen content The dissolved oxygen content in the steel bulk is a key parameter in refining during steel making process.f) is built up when different oxygen activities are sensed by the two electrodes. An electromotive force (e. The thermocouple attached to the sensor measures the temperature of the system.m.f to obtain the oxygen activity which is then displayed on the screen of the equipment.m. 26 . A calculation is generated automatically using the measured temperature and e. The usual slag practice for ladle refining is either synthetic slag blend 1 or 3(table 2). For SiO2.01% and 2.59 0.4.0 RESULTS AND DISCUSSIONS 4.31 Synthetic slag 1: 65%Lime&35% Alumina.5%.9% with relative deviation of 4. Synthetic slag 3: 73%Lime&27% Pure Alumina (Measurement is in wt-%) 0.05 0. FeO and Al2O3.48 0.09 . Synthetic slag 1 and 2 are mixtures of 65% Lime / 35%Alumina and 60%Lime / 40% Alumina respectively.52 25.13 68.14%. The change is quite high for some oxides while it is low for others.8 %.92 2.110 0.47% respectively.13 Synthetic slag 3 4.50 25.23 22.62 0.49 2.00 0. Synthetic slag 2: 60%Lime&40%Alumina.14 Synthetic slag 2 62. while CaO is lower. it has a higher mass than the previous slags (1300kg). It could be seen from table 3 that the range of wt%CaO is between 49.10% while MnO is 0.10 . the average top slag composition before vacuum treatment for all the heats is higher than the synthetic slag blends added.18 0.2 Top slag compositional changes The analysis of the compositional variation of topslag before degassing for the 12 heats followed during the thesis work is given below.90% . MgO.75 5. 27 . The mass of the slag varies between 800 and 1000kg based on the degree of sulphur removal for the different steel grades. Table 2: The Initial composition of three different synthetic slags Composition CaO Al2O3 SiO2 MgO S TiO2 FeO MnO Synthetic slag 1 66.1 Synthetic Slag Composition The synthetic compositions of the mixture of the different slag formers used at the steel mill during the trial sampling are given in Table 2.04 0.71 0. MnO. The range of SiO2 is between 5.64.05 0.12 0. and wt%Al2O3 is between 21.31.79 2.77 4.04 0. Synthetic slag 3 contains 73% Lime and 27% Pure Alumina. the compositional change of the top slag after heating and before vacuum treatment for the 12 heats is shown in figure 16.3. 31 10 9.30 49.60 %MnO %CaO 0.70 24.40 26.37 4.0 30 60 27 7.10 31.70 0.81 2.1259 1639 1610 1606 1597 1625. are connected to high proportion of lime in the synthetic slag blend and also high mass of the synthetic slag (this is a common practice for high clean steel which requires extreme sulphur removal).5 55 24 50 5.80 10.09 Mean 6.10 5.1205 3.00 59.90 3.20 1.40 8.50 58.20 11 7.30 4 6.70 8. Table 3: The composition of top slag before degassing for composition Charge %SiO2 1 2 3 6.40 9 5.43 1.8150 4.40 56.90 0.40 0.90 25.C aO % A l2O3 % 33 65 SiO2 % 10.18 73.14 0.00 6.40 28.66 2.91 2.0263 3.73 3.00 5.5326 3.60 59. The lower extreme values are peculiar for heats with high oxygen activities ao at tapping.24 3.4140 1610 1596 1624.60 25.26 3.50 0.18 57.6064 2. which implies a low yield of Al and Si at tapping and also higher potential to retain some deoxidation products as inclusion in the steel bulk or on the ladle wall 28 .10 60.50 2.00 27.51 The composition is measured in wt-% %Al2O3 %MgO %FeO ao(ppm) Temp °C 1.7 1577.7 1.90 28.80 4.87 26.49 6 7.02 8. and represent the mean and median of the data set.0369 3.60 1.70 5.70 63.80 64.01 6.50 26.9 1608.90 0.1400 2.92 0.20 6.20 0.61 2.00 0.24 3.21 0.33 1.92 Std dev 1.60 1.50 56.00 56.76 5.47 9.30 6.28 3.03 34.9 1618.65 2.01 55.20 0. 20.62 127.00 21.6 The higher extreme values for the CaO in the box plots (though not considered as outliers for the distribution).4036 2.90 0.50 62.13 12 6.50 27.17 Rel dev.20 7.77 7 5.23 8 6.0 21 MnO % 4 FeO % 4 3 MgO % 8 3 6 2 2 1 1 0 0 4 2 Figure 16: Box Plot-Investigating the variation in the top slag composition before Degassing where represents mid spread of the data (50% of the heats).46 0.84 5 6.90 26.10 0. 9 %MgO 7 Before Degassing After Degassing 5 3 1 45 50 55 60 65 % CaO Figure 17: MgO pick up from the refractory into the top slag 29 . they are refined with synthetic slag former of high mass and low initial SiO2. It can be clearly seen from figure 17 that the solubility of MgO refractory into the topslag varies with CaO content of the top slag. age of the ladle in use.until ladle refining stage when they are removed to the top slag. This reduction (equation 21) is aided by high %Al and low ao of such heats. lime saturation of the top slag and it also depends on the slag former blend. This is an indication that their compositions in the topslag are not controlled by the variation in the slag former blend. then the MgO content of the top slag before vacuum treatment will be very low due to the low content of MgO in it. Newly lined ladles have greater potential to wear than old ladles though they give better thermal resistance and heat conservation than the old ladles. FeO and SiO2 have high relative deviation with wide spread of the values and most of the values close to one extreme end. depict special heats with high purity requirements. The upper extreme values for these oxides contents are results of high ao at tapping. The trend for the variation of MgO from 2. It was observed that the ladle age is also an influencing factor for the MgO content of the topslag before vacuum treatment. lime saturated topslag has a low solubility potential of the refractory and vice versa. and it in turn favours good desulphurisation. Al/O/ Al2O3 equilibrium before vacuum degassing and also the quantity of carry over slag remaining after the mechanical slag removal. as it depends on the amount of EAF slag remaining after slag removal. The SiO2 content of the slag of such heats is reduced further during vacuum treatment as the interaction between slag and steel degassing became improved. especially for SiO2. The lower extreme values.5 to 8.2% is a little bit compounding. If pure Alumina is used. On the contrary MnO. For %Al2O3. the outlier is an uncommon blend of slag former (68% Lime and 32% pure Alumina) which contains very high %Al2O3 . In the calculation. Furthermore. since their initial mass in the slag formers used during refining are small. before vacuum treatment. This support earlier observation on the large deviations of SiO2 and MgO contents of the topslag before degassing. The mass balance procedure for a heat could be followed in appendix X. the mass of the CaO content of the synthetic slag was assumed to be constant throughout the ladle refining. For Mn. mass input was not equal to mass output due to the influence of the carry over slag. The higher values of Mn in Table 4 are peculiar to heats with high manganese contents. The results shows that extra slag was often added to the steel during heating and inductive stirring. ladle glaze and also EAF slag that clustered on the ladle walls. The optimum inductive stirring power of about 1000W together with the new top slag composition often enhanced the lifting up and absorption of the inclusions (from deoxidation products attached to the ladle wall).4. The changes in the wt%CaO content of the slag was thus used to calculate the extra slag which floats to the top slag and the new top slag mass. It could be seen that excess Al. Si as well as Mg appear into the system in all the heats in the mass balance made just before the vacuum treatment. 30 . this could be taken as an error in measurement of Mn alloy. Table 4 shows the mass difference of some selected elements. In the mass balance. Also the CaO content of the dilution slag can be ignored because of its small mass compared to its content in the synthetic slag. The elemental mass difference in the steel and top slag could be said to be a result of the carry over slag whose composition is unknown. (With the exception of heat 3 which could be due to measurement error). an attempt was made to calculate the elemental mass balance between the steel and slag for each of the heats just before vacuum treatment during the ladle refining. and these values are less than 5% of the total mass of the alloy added at such heat.3 Mass Balance A mass balance was done to investigate the probable mass of dilution slag which was transferred to the top slag after slag removal. as the calcium content of the steel is so low and thus has a very low thermodynamic potential to react. this could be substantiated. into the top slag. the additional mass though very small has a meaningful influence on the top slag composition before degassing. 81 0.13 0. and thus mass balance was incomplete *All calculations are in Kg The mass balance done in this work. Si yield at deoxidation.17 0.02 0.04 Al 26.98 4. calculated mass of carry over slag.02 -0. An overview of the model obtained is shown in figure 18 and 19. The assumption of fixed mass of CaO in the slag before degassing also influences the result of the mass balance.46 0.01 0.05 -0. 31 .75 16.08 2.27 7.32 -0.06 0. To increase the accuracy of the PLS analysis 12 extra heats from previous experiments carried out during ladle refining in Ovako were added to the 12 heats investigated in this thesis work. On the contrary.40 2.68 32.32 11.66 -0.26 26.09 3.56 6.69 -0.02 18. The predictors include Al yield.83 Mg 27.09 -3.04 11.90 25. mass of Si and Al metal added at deoxidation. the figure also shows that heats with either high slag former addition or low high %C at tapping have tendency for an increasing CaO content and decreasing SiO2 content of the top slag before degassing. The PLS modelling was done using SIMCA-P +10.63 -3.39 39.94 -50.71 0.32 4.71 0.06 0.65 -2.00 0.90 8.92 S -0.71 Mn 6.89 1. from figure 18 it could be seen that heats with low %C at tapping.13 23.17 0. the values are not extremely precise but the trend is good for analysis.90 6. lower yield of deoxidants at tapping and also higher amount of extra slag have a tendency for an increasing SiO2 content of the top slag and a decreasing CaO content.53 61.37 9. temperature at tapping and carbon content at tapping (oxygen potential).29 14. The SiO2 and CaO composition of the top slag for the 24 heats were set as the dependent variables while all other variables were set as predictors. The predictors also include the SiO2 and CaO content of the removed slag and mass of slag former added.35 26.81 25.15 -16.01 0.24 14.51 0.77 Ti 0.67 Ca 0.56 Extra Slag 146 256 74 130 165 82 164 93 137 97 149 *Heat 5 was not recorded because no sample was taken at sample point 4. It is difficult to calculate a perfect mass balance at some points because the reactions proceed rapidly until equilibrium is achieved.4 Regression Analysis for the Top Slag Variation A partial least square (PLS) regression was done to further investigate and probably model the factors influencing the variation in the composition of the top slag before degassing.Table 4: The mass balance between slag& steel of selected elements before vacuum treatment Heats 1 2 3 4 6 7 8 9 10 11 12 Si 15.72 -38.22 -1.52 15.31 8.46 0.10 16.12 30. 4.79 22.21 20.47 4.78 -1.40 1.63 5. only gives an idea of an upward flow of oxides from the steel to the topslag as well as the reduction of oxides into the steel.02 0.91 8.88 14.01 0.58 20. 50 -0.00 Si Yield Al Yield -0.80 Slag forme 0.50 0.10 0. 2] 4 N3589-803Q 3 2 N5944-277Q 1 t[2] N3614-803F N5902-804Q N6192-803F N3620-803Q N3677-803Q N3634-803Q N3601-803Q N3602-255G 0 N6067-803Q N6206-803F -1 -2 N3622-803F N6145-143A N6040-123A N5857-824B N6174-803F N6236-824B N6052-280T N6066-803F N6204-825B N6208-803J N5858-256G N6175-826B -3 -4 -4 -3 -2 -1 0 1 2 3 4 t[1] Figure 19: Score Scatter plot of the observed heats 32 .60 w*c[1] Figure 18: Loading scatter plot of the investigated parameters M1 (PLS) t[Comp.40 0. the heats with high slag former are grouped together in a direction of low SiO2 contents (high CaO content) while the heats with low %C at tapping (high ao) tends in the opposite direction favouring high SiO2 content (low CaO content) of the top slag. 1]/t[Comp. 2] 0.10 0.20 -0. 1]/w*c[Comp.30 0.40 CaO_degas Al(kg) w*c[2] 0.10 Temp 0.10 SiO2_degas -0.A plot of the influence of the independent variables on the heats is shown in figure 19 (score plot).60 0.30 SiO2 CaO -0.50 -0.30 0.70 0.30 -0.20 0. X Y M1 (PLS) w*c[Comp.00 0.20 0.40 -0.50 0.40 Extra slag -0.20 Si(Kg) C -0. this parameters include the description of the ladle glaze.The contribution of each of the independent variables to the model for the prediction of the SiO2 and CaO content of the top slag is shown in figure 20. the model was also mostly described by the same important parameters as observed for CaO and SiO2. 2] VIP[2] 2 1 Temp Si(Kg) CaO SiO2 C Al(kg) Al Yield Si Yield Slag forme Extra slag 0 Var ID (Primary) Figure 20: VIP plots of the predictors in the model In summary the model created shows a fairly good explanation of 0. amount of the synthetic slag former added. M1(PLS). yield of the deoxidants into the steel and the carbon content at tapping (oxygen potential). mass of the EAF slag removed and mass of refractory wear. The reason for this is that. VIP[Comp.34. some other important variable parameters were not involved in the PLS regression. This implies that the model is unreliable to predict the composition of the top slag before degassing for any arbitrary heat besides the heats observed. 33 . but it has a poor predictability of 0.64 for the variation of the dependent variable (CaO and SiO2) in all the observed heats. The most important parameters influencing the top slag composition before degassing as shown by the VIP plot below are. Similar regression was done for the prediction of Al2O3. amount of carry over slag. amount of EAF slag tapped. An attempt was made to create a model and also modify the existing ones in order to estimate the ao at any given point during the ladle refining. A Engh (8). The second model assumed equilibrium between Al and O dissolved in the steel and Al2O3 inclusion in the steel bulk.4. A control of the desulphurisation process is impossible if the oxygen activity is not known. Model 2 and 3 gave fairly close values compared with measured values while model 1 shows a high discrepancy. 34 . temperature and %Al in the steel) to predict the ao at a particular temperature and within an Al range. for this model the activity of Al2O3 inclusion was assumed to be 1 since at this stage of refining ( before degassing) it is valid to consider that the inclusion is Al2O3 saturated (15). The values of the interaction coefficients used were taken from T. Appendix XI shows graphical relationship between ao and %Al in the melt at different temperature. Three models were established for online prediction of ao and they were also compared with the measured values. Figure 21 shows a comparism of the three models with the measured ao values. In the third case a model was created using several existing online process data (measured ao. The first model assumed equilibrium between Al and O dissolved in the steel melt and Al2O3 in the slag (4) . The formula obtained in the model fit in appendix XI was used in the third model calculation. Ohta and Suito expression in equation (17) was used to calculate the Al2O3 activities in the slag while Wagner's expression in equation (16) was used to calculate the Al activities in the steel.5 Oxygen Activities An important thermodynamic parameter which influences the desulphurisation process apart from slag composition is the oxygen potential of the slag-steel system (equation 13). 5.1363x .4968 4.0E-04 Al2O3 =1 Data Measured ao 2.0E+00 0 2 4 6 8 10 12 14 Heats Figure 21: Measured and calculated oxygen activities before degassing It could be seen from figures 21 and 22 that model 2 which assume equilibrium between Al/O/Al2O3inclusions has a quite close pattern with the measured ao values and also has a high degree of explanation for the deviation of its values from measured value.00E-04 3.00E-04 4.1E-05 R2 = 0.0001 R2 = 0.0E+00 1.00E-04 6.4968x + 0.0E-04 0.6223 Ohta&suito 2.0E-04 y = 0.8197 3.0E-04 y = 0.0E-04 1.0E-04 y = 0.00E-04 2.0E-04 0.00E-04 5.5.0E-04 Ohta&suito 3.00E-04 Measured ao Figure 22: Refitting Oxygen activities Models 35 .7739x + 2E-06 R2 = 0.0E-04 Al2O3 =1 Data 1. It has a good Calculated ao agreement with measured values.0E-04 ao(ppm) 4. Sulphide capacity was calculated using Young et al expression.00E-04 5. written in equation (12) but in few cases when optical basicity is very close to 0. The calculated Ls gives the probable sulphur distribution at equilibrium. 4.8. Sosinky & Sommerville expression was used due to better correlation (14).00E-04 ao (ppm) 4. 6.00E-04 0. while measured Ls gives the actual distribution at the prevailing kinetic conditions. Figure 24 shows the values of measured and calculated sulphur distribution ratio after vacuum treatment.00E-04 Measured ao 2.00E+00 0 2 4 6 8 10 12 14 Heat Figure 23: Modified oxygen activities Models For online utilisation of ao values.00E-04 Ohta&suito Al2O3=1 Data 3. A perfectly 36 .00E-04 1.A refit of these models was done and the modified models gave better ao prediction as seen in figure 23 below. Ls was calculated using equation (13) where fs was obtained with Wagner's expression in equation (16) and ao was calculated using Al/O/Al2O3inclusion equilibrium. it could be inferred from the investigation above that model 2 gives a fairly accurate result with better predictability. is another important parameter in the modelling of sulphur removal in steel making. as earlier mentioned.6 Equilibrium sulphur Distribution The slag-metal sulphur distribution ratio Ls after desulphurisation. For most of these heats the average flow rate of argon gas in either/both porous plugs was lower than 45ltr/min as opposed to about 80ltr/min for others and 100ltr/min suggested by Hallberg et al (17) . this influences the measured Ls.linear correlation could not been observed from figure 24 because equilibrium was not reached after vacuum treatment for few heats. This could be explained by kinetic reasons of either short time or poor interaction between the reacting phases.e. 37 . i. assuming favourable kinetic conditions such as low vacuum pressure. et al (4). this is supported by previous investigation done by Andersson M. The optimum vacuum pressure (<5 torr) was always attained during the plant trials but an investigation of the gas flow for all the heats shows that argon gas flow rate has a major influence on the success of the desulphurisation. Another reason could be that the sulphur composition of the slag after desulphurisation is inhomogeneous. 1200 1000 Measured Ls 800 600 400 200 0 0 200 400 600 800 1000 1200 1400 Calculated Ls Figure 24: Distribution of sulphur between slag and steel after Vacuum treatment against calculated Ls The heats in figure 24 with lower values of measured Ls compared to calculated Ls have poor gas stirring. Calculated Ls is the sulphur partition value at optimum desulphurisation condition. optimised argon gas purging and good viscosity. it could be seen that the tendency of having a very high DD is favoured by high mass of slag former. 12 extra heats from previous research on ladle refining done at Ovako were added to the 12 heats investigated in this thesis. The SiO2 content of the top slag has a negative influence on DD. and this is as a result of unusually low Al2O3 and very high CaO content in the top slag and also very poor argon gas flow rate.772). Ar2). Similar to the PLS analysis done earlier for the variation in top slag composition before degassing. time. while the predictors are.variable contributions in each heat. The score plot of the observed heats in figure 26 shows an outlier heat. oxygen activity (ao). basicity (B1). The influence of the cross interaction between CaO and Al2O3 was also included in the model. the dependent variable was set to be the degree of desulphurisation (DD) (definition can be seen in equation 20). An increasing basicity is also very important to obtain good desulphurisation but it requires high slag mass to achieve an extreme desulphurisation. An overview of the model is shown in figure 25 and figure 26. The degree of desulphurisation DD is well modelled by the x-variables due to its high degree of explanation (0. From the loading plots of the predictor in figure 25.7 Regression Analysis for the Desulphurisation Process A multivariate data analysis was carried out to investigate the important parameters during the process of desulphurisation and their influences. %Al in the steel and the cross interaction between CaO&Al2O3. In the PLS modelling of the desulphurisation process.899) and also a good predictability of (0. temperature (temp). coefficient of sulphur activity in the steel (fs) and slag composition. the DD predicted by the model from the x-variable parameters of this heat does not correlate with measured DD. to increase the accuracy of the prediction of the modelling. this is explained by the x. DD = [%Si ] − [%S f ] X 100 [%Si ] − − − − − − − − − − − − − − − − − − − − − (20) Where [%S]i is the Initial sulphur content of steel before degassing while [%S]f is the final sulphur content of steel after degassing. mass of slag former. 38 . This will enhance the optimisation of top slag composition for precise sulphur removal with consideration to other factors. aluminium content of the steel [%Al]. The figure also shows the grouping of all heats into extreme sulphur removal and low sulphur removal. CaO/Al2O3 ratio. average argon gas flow rate in porous plug 1 and 2 (Ar1.4. longer time of degassing good argon gas flow through the porous plug. 40 SiO2 ao Ar 1 0.10 Slag forme CaO*Al2O3 CaO/Al2O3 0. 2] 3 N5858-256G 2 N3622-803F N6204-825B N6145-143A N6052-280T 1 N3602-255G t[2] N3614-803F N5944-277Q N6040-123A N3601-803Q N3620-803Q N3677-803Q N6067-803Q N3634-803Q N6236-824B 0 N5857-824B -1 N6192-803F N3589-803Q N6066-803F N6175-826B N6174-803F N6208-803J -2 N6206-803F N5902-804Q -3 -6 -5 -4 -3 -2 -1 0 1 2 3 4 5 6 t[1] Figure 26: Score Scatter plot of the observed heats The contribution of each of the independent variables to the model for the prediction of the DD is shown in figure 27.X Y Cross M1 (PLS) w*c[Comp. 2] Ar 2 0.20 0.20 -0.10 CaO Al2O3 %Al -0.30 DD Temp 0.40 -0. The most important parameters influencing the DD as shown by 39 .30 0.40 w*c[1] Figure 25: Loading scatter plot of the investigated parameters M1 (PLS) t[Comp.10 0.00 -0.30 fs -0. 1]/w*c[Comp.20 Time w*c[2] 0.10 B1 0. 1]/t[Comp.00 0. 00 Time 0.60 0. slag composition. mass of slag former. %Al. time. 40 .00 0.00 1. temperature. Oxygen activities ao is dependent on temperature. It is expected that high ao should have a negative influence on DD but this could not be clearly seen on the model overview. Heats with longer degassing time usually commenced at higher temperature for the reason of favourable kinetics during the length of degassing.60 1. M1 (PLS) VIP[Comp.the VIP plot of the model are.20 Figure 27: VIP plots of the predictors in the model An observation from this PLS regression analysis worth mentioning is the influence and importance of the ao in the model. oxygen activity and argon gas in the second porous plug.40 VIP[2] 1.20 1. so it is difficult for PLS model to show the precise influence of ao on DD. this however made it difficult to see the expected influence of ao on DD in this simple model. since the degassing for all the heats were not carried out at the same temperature. basicity.80 1.80 0. 2] 2.40 CaO/Al2O3 fs CaO Al2O3 ao SiO2 B1 CaO*Al2O3 Ar 1 Ar 2 %Al Slag forme Temp 0. Each heats have two points on the curve. T. If the temperature is high (which implies high ao). The smooth curve on the graph is the equilibrium relationship for Al reduction of SiO2 from lime saturated calcium aluminate slag at temperature close to 1600˚C. 41 .4. Higher SiO2 content of the top slag before degassing (due to the dilution of the synthetic slag by carry over slag) contributes to the oxygen potential of the system especially when %Al in the steel is low.8 Equilibrium Condition during Vacuum Treatment A study of the possible thermodynamic equilibrium which has influence on the desulphurisation process was examined. The reduction reaction is shown in equation (21). as explained by E. the forward reaction is favoured if the Si content of the steel is low and the Al content is high and with a rigorous argon gas stirring (20). (SiO2) + 4/3[Al] = [Si] + 2/3(Al2O3) ----------------------------------------.(21) For the 12 heats investigated. This condition is not favourable for good sulphur removal. the point with higher Al represent the condition before degassing when equilibrium has not been achieved while the corresponding point with lower Al depicts equilibrium condition after degassing (though it was suspected that few heats did not attain equilibrium with the kinetic conditions that prevailed during the process). The points on figure 28 explain the drift of the system towards equilibrium during degassing. and %Al is low. the silica content in the slag might increase during the vacuum treatment. Turkdogan (20). the influence of the above mentioned equilibrium condition on sulphur removal is shown in figure 28. The desulphurisation reaction during the vacuum treatment shown earlier in equation (18) is influenced by reoxidation reactions and also the equilibrium between Al/Si content of the bulk steel and the SiO2 content of the slag. Heats with high ao before degassing have the tendency of increasing SiO2 of the slag and thereby limiting the extent of the desulphurisation even if the slag is lime saturated. 42 .120 3 8 0.000 0. Heats with high %Al before degassing have low ao and have higher potential for the reduction of the slag and consequently giving a favourable condition for desulphurisation to proceed.020 0.060 1 6 11 0.080 [% Al] 2 7 12 0.160 4 9 Figure 28: Aluminium reduction of SiO2 from Lime saturated molten slag during degassing From figure 28 it could be noted that all the heats are moving towards the smooth equilibrium curve as the vacuum treatment proceeds. Heats with low %Al have the tendency for increasing SiO2 content of the slag and increasing oxygen potential of the system which is unfavourable for sulphur removal. some final points are yet far away from the curve either due to lower reaction temperature compared to that of the equilibrium curve or equilibrium has not yet been achieved before the process was stopped.80 70 60 SiO2/Si 50 40 30 20 10 0 0. The initial ao activity before degassing is also another important parameter which influences the equilibrium drift in the plot.140 0.040 Equil Lit 5 10 0.100 0. 43 .Final Sulphur content of steel after degassing (%S)i .Final Sulphur content of slag after degassing Ls . The mass difference of sulphur in the steel before and after degassing was equated to the mass difference of sulphur in the slag.9 Equilibrium Sulphur Content in the Bulk steel A mass balance was made in terms of sulphur content of the system at equilibrium.4. similar reasons hold for the observed variation in the measured and calculated values of Ls explained earlier. average extra slag mass of 200kg was added to the top slag for all heats since a range of about 150-250kg was estimated in the conditional mass balance done earlier. To simplify the calculation of the equilibrium sulphur. M s [% S ]i − M s [% S ] f = M sl (% S ) f − M sl (% S )i [% S ] f = M s (% S )i + M S [% S ]i − − − − − − − − − − − − − − − − − − − − − −(22) M Sl ⋅ Ls + M S Ms .Mass of slag [%S]i -Initial Sulphur content of steel before degassing [%S]f . Figure 29 shows that few heats have higher measured [%S]f values after degassing compared to calculated values.Initial Sulphur content of Slag before degassing (%S)f . in order to project the sulphur content of the steel after vacuum treatment.Sulphur Partition It should be noted that the compositional change in the top slag was considered in the calculation of Ls since mass change is of no effect on it.Mass of steel Bulk Msl . The amount of slag carry over could be reduced to an insignificant amount by improving the ability of the first slag from the EAF to absorb inclusion and entrapped glaze.020 0.005 0. perhaps due to poor argon gas stirring or time factor.010 0.010 0.005 0. other models such as 'IRSID' and 'Thermoslag' could have been used as well but their parameters were not accessible. This is as a result of few important parameters which could not be measured. 4.000 0.025 Measured [%S] f 0.015 0.025 Calculated [% S]f Figure 29: Calculated and measured equilibrium sulphur in the steel The heats with values far away above the equilibrium line are the same heats with wide variation in Ls. It should be noted that some of these deviations observed in the calculated parameters could be due to the model used in calculating the sulphide capacity of the slags.015 0.000 0. An alternative measure to achieve this result is 'extra slag practice'.10 Optimisation of the top slag composition The regression analysis made for the top slag composition before degassing and other empirical process investigation shows a very low degree of the prediction of the carry over slag composition. this however made the optimisation of the top slag for precise sulphur removal more challenging.0. 44 . equilibrium was not achieved after vacuum treatment. A short inductive stirring before slag removal is also necessary to aid the separation of these entrapped oxides into the floating slag.020 0. A short inductive stirring is necessary to remove the ladle glaze and other oxides.The extra slag practice involves the addition of lime (200-400kg). and also enhance the upward transport to the slag at the top of the vessel. This practice will enhance the accurate estimation of slag former with right mass and sulphide capacity for a precise sulphur removal since dilution of the new synthetic slag would have been reduced to an insignificant level. 45 . during tapping to increase the activity of CaO and thus improve the ability of the EAF slag to absorb the entrapped oxides in the steel. this however result in low MgO content of the topslag before degassing as slag with high CaO has low tendency for the dissolution of the refractory. • A number of heats has lower sulphur partition ratio after desulphurisation compared to the calculated values due to poor argon gas flow. They are easily reduced by Al. including heats with low oxygen potential at tapping. mass of carry-over slag. It was also noted that heats with high oxygen potential before tapping and low mass of synthetic slag former. this is also substantiated in the regression analysis made.1 Conclusion The main factors influencing the top slag composition before vacuum treatment include. The variation in the top slag composition and the desulphurisation process for the heats investigated. This is an influence of the unknown mass of slag and oxides remaining on the ladle wall or entrapped in the bulk steel after EAF slag removal. could be summarised below • All heats have at least 100% increase in the SiO2 content of the top slag before degassing. ladle glaze and amount of EAF slag left after slag removal. 46 . where the yield of silicon from FeSi into the steel is high. oxygen content of steel at tapping. This necessitated an alternative solution of extra slag practice to improve the absorption of oxides in the steel bulk. Heats for high clean steel. • The most important factors influencing top slag composition before degassing are amount of slag former added. These two oxides appear to be low when low oxygen activity is achieved after deoxidation at tapping or when the %Al content of the steel is very high. oxygen potential and the yield of the deoxidants at tapping.0 CONCLUSION AND RECOMMENDATIONS 5. • MgO obviously comes from two major sources. have very low MgO and high CaO in the synthetic slag blend. • The PLS model created has a very unreliable predictability for the top slag composition due to lack of other important parameters. have an tendency for increased SiO2 content in the top slag before degassing • MnO and FeO in the top slag before vacuum treatment are also traced to slag or oxides entrapped in the steel or on ladle walls. carry over slag and refractory erosion. extent of deoxidation at tapping.5. • The improvement of the argon gas stirring for optimum utilisation of the sulphide capacity of the slags should be investigated. 5. to really know the oxygen level in the steel bulk and avoid additional estimation of extra aluminium metal mass by operators. for heats with high final sulphur requirement. This will decrease the degassing time and also contribute to the expected result for precise sulphur removal using slag composition control. • Further research should be carried out on the mass of lime to be added during tapping to improve the ability of the EAF slag to absorb entrapped oxides in the steel bulk.2 Recommendations The following praxes highlighted below are recommended based on the investigation made in the research thesis and the prevailing process practices at the steel plant. • It is strongly recommended that further investigation should be carried out on deoxidation at tapping as the process seems to be inconsistent. to reduce loss of sulphur into the slag during vacuum treatment. % Al. the argon gas flow and inductive stirring effect during the vacuum treatment must be optimised as well. 47 . It is suggested that a steel sample should be taken shortly before tapping after which there will be no further oxygen blowing. • It could be a better practice to add extra sulphur into the system only after vacuum treatment. vacuum treatment time. In some instances.• The second regression analysis made shows that the sulphur removal can be optimised by controlling the following parameters. and also the material handling of the deoxidants should be improved. • To achieve a precise sulphur removal with an optimised top slag composition. low ao could not be achieved due to Al/O/Al2O3 equilibrium. Consistent and accurate amount of FeSi should be added during tapping. oxygen activity in the steel before degassing and argon gas flow rate. mass& composition of the top slag. Fredrich Martinsson. Encyclopedia Britanica.REFERENCES 1. Jonsson. 48 .britannica. D.com/EBchecked/topic/564627/steel#. H. KTH. Björklund. Turkdogan. 9. E. Malin Hallberg. Lage T. Mselly M. LTU. 11. No 4. World steel Association. The insititue of Materials 1996. Abel Engh. Bo Björkman. Application of Sulphide Capacity Concept on High basicity Ladle Slags Used in Bearing Steel Production. Lage T. applied for removal of sulphur during the ladle treatment. 14.org Feb.worldsteel. Margareta Andersson. pp312-324. Förbättring av svavelrening och avskiljning innan samt efter vakumbehandling genom spolning med argon vid tillverkning av rent stål. 40 (2000). Optimisation of Ladle slag Composition by application of a sulphide capacity Model.No. Material Technology 34(6)387(2000) 2. http://www. Savov. Jönsson. 11. Equilibrium conditions between Slag and Steel and Inclusions during Lalde treatment. J. Vol. Edited by Verein Deutscher Eisenhuttenleute (VDEh) 15. section2 .T.I. Andersson. Iron and Steel making course compendium.com 4. Pär G. Iron and Steelmaking. Pär G. pp. 1080–1088.pp1289-1302. Jonsson. Nzotta. A model for Multicomponent reactions between metal/slag using Thermo-calc. 34. ISIJ International. 10. 5. 12. 2009 3. Vol 39 (1999) No 11. L. pp 1140-1149. Slag Atlas second Edition. http://www.I. Pär Jönsson. 8. T. ISIJ International Vol. Janke. Margareta Andersson. E. Schulz . ISIJ International. Fundamentals of Steel making. Scrap based steel production and recycling of steel. Vol 41 (2001). 7.ovako. A thermodynamic and Kinetic Modelling of Reoxidation and Desulphurisation in the Ladle Furnace. P Jönsson. No. Principles of Metal Refining. Ovako Intranet. Process Metallurgy division. The Use of Fundamental Process Models in Studying Ladle Refining Operations. http://www. Jönsson. 11. 1996 6. Margareta A.J Weddige. 13. Iron and steel making February 2000. Oxford University Press New York. Master Thesis KTH. Pär Jönsson. Anna Boström. 2007. Licentiate thesis 1997. L.. Malin Hallberg. Iwase M. Sawa.N Tripathi. 18.pp 341-347. 49 . Improved Control of sulphur and Hydrogen Refining Using Process Models in Production.. Jönsson. M. No 3 pp 255-308... A Sandberg and Du Sichen. Nzotta. Canadian Metallurgical Quarterly. L. Du Sichen S. Ohnuki K. T. Pär Jönsson. Ladle Glaze. Jonsson and P. The activities of FeOx CaO-SiO2-Al2O3-MgO-FexO slags at 1723K. Nzotta.9 No 3. Margareta Andersson. Jonsson. 20. 2001. ISIJ International. Mselly M.T Turkdogan. Slag-Metal Reactions during ladle treatment with focus on desulphurisation.a major source of non metallic inclusions in Ladle treatment of Tool Steel. JernKontorets Forskning Proceedings May 2004.. 38 (1998). 19. pp 224-232 17.. Retrospect on Technology Innovations in ferrous Metallurgy. Iron and steel making 2002 vol. Malin Hallberg.16. E. Seetharaman. Vol 40. Hasegawa M. 1170. 21. Steel Research International 76(2005) No 5. Sulphide Capacities in Multi component slag systems. Kishimoto T. N. 3 12.2 41.90 21.60 38.20 1.07 0.19 0.28 3 15.80 16.10 5.20 35.60 14.90 1.51 0.50 25.08 0.20 0.44 22.9 36.6 10 14.06 0.6 0.2 27.70 0.50 10 18.40 5.84 0.11 0.60 16.12 28.7 26.7 5.5 Sample after Tapping 1 2 3 14.3 1692.90 15.57 3.50 4.36 23.17 0.2 12 22.44 8 9 19.18 4.6 5.56 18.70 TiO2 % CaO % Al2O3 % MgO % FeO % 0.80 23.7 25.09 0.14 0.11 0.08 0.80 30.47 11.28 0.3 10.30 11 18.30 11.38 29.3 22.62 12.30 5.60 0.1 11 14.10 2.13 9.68 0.29 0.09 5.10 0.60 28.18 0.38 4 20.70 30.4 7 17.90 2.60 13.076 0.80 7.1 4.50 7.40 24.053 0.30 12.60 9 23.00 3.88 23.4 5.4 13.0 11 16.9 6.8 Sample Before Slag Removal 1 21.00 20.23 6.7 5.51 5 10.24 2 17.50 23.60 22.11 35.46 44.3 4.3 3.27 0.19 0.2 12 18.00 1.04 0.48 9.70 22.1 49.2 27.6 11.20 29.8 10.16 0.33 0.08 4 16.7 12.21 0.70 2.20 7 15.6 Continue on next page 50 .7 10 14.20 27.8 0.07 0.60 31.27 30.1 20 6.70 4.7 6.2 14.5 0.20 24.70 22.50 2.1 12.61 6 17.25 0.60 40.90 17.01 6 7 8 9 11.80 15.6 13.20 3.49 0.90 19.18 0.11 0.90 20.09 0.7 15.10 0.70 12 19.90 29.2 1703.36 6 20.6 2.90 0.09 5 11.9 25.9 12.51 0.3 5.8 0.93 5.9 48.30 4.80 22.14 0.18 0.70 33.71 23.0 10.10 28.10 0.54 0.90 2.8 17.37 23.0 7.0 45.20 26.48 0.60 3.00 2.7 5.8 0.52 0.2 2.APPENDICES Appendix I: Slag composition of all heats Heat SiO2 % MnO % S % Sample in the EAF before Tapping 1 2 3 4 5 12.34 34.12 0.10 0.40 20.30 ao(ppm) Temp˚C 136 N/A 632 159 928 1694 1730 1713.51 0.38 22.22 0.11 0.30 23.1 5.16 0.55 8 15.54 0.5 3.20 25.8 15.20 0.4 6.6 8. 52 0.46 0.77 5.70 6.40 1.90 0.0370 2.90 0.10 7.10 0.80 0.00 29.49 7.61 1.30 35.20 5.40 0.32 1.13 0.00 12.10 1.10 0.80 0.40 5.14 0.60 3.50 2.6 1512.00 0.10 60.00 59.38 1.00 26.05 6.70 55.47 0.1259 Temp 1610 1596 1625 1639 1610 1606 1597 1626 1619 1578 1609 51 .76 3.00 29.37 0.46 9.20 0.10 0.7140 0.00 21.50 0.40 59.20 0.11 0.31 0.70 1.60 29.56 0.70 0.90 8.30 6.80 52.10 60.67 0.20 0.00 6.70 7.8150 4.81 2.21 0.19 0.2865 1.24 3.35 0.14 57.09 After Degassing 8.13 0.0609 0.6765 1535 1564 1521.14 0.01 55.07 0.05 at completion of Refining % TiO2 % CaO % Al2O3 % MgO % FeO % 0.13 8.10 49.90 0.50 26.24 10.Heat Sample 1 2 3 4 5 6 7 8 9 10 11 12 Sample 1 2 3 4 5 6 7 8 9 10 11 12 Sample 1 2 3 4 5 6 7 8 9 10 11 12 SiO2 % MnO % S Before Degassing 6.20 6.3340 1.70 5.20 7.78 28.21 0.27 5.4036 1619 1.30 1.5 1546.00 27.28 3.20 28.13 6.19 0.50 59.72 0.78 7.4 1537.91 2.20 7.52 0.30 28.60 59.30 27.90 25.16 52.21 0.15 0.17 0.21 56.50 62.27 0.50 27.72 0.77 1.4036 2.66 2.16 0.15 0.70 24.60 0.20 8.20 0.4140 5.40 0.70 5.13 0.70 0.60 59.70 6.77 1.27 0.00 0.90 25.00 3.70 21.00 6.80 52.21 56.70 8.19 0.30 1.32 8.40 56.50 56.4850 1.1205 3.60 6.10 0.40 26.05 0.41 0.9 1577 1541 1540 1515.14 5.70 0.60 26.90 58.50 3.30 1.10 0.30 34.18 6.31 9.00 0.60 6.9190 4.10 0.5326 3.10 4.60 25.6064 2.1400 2.12 0.17 0.90 3.50 0.60 56.10 0.40 7.84 6.23 0.6400 3.20 0.07 0.17 0.70 63.40 7.10 56.0263 3.40 28.40 26.60 29.60 0.33 1.77 1.20 1.00 7.04 12.15 0.86 0.30 0.43 0.00 56.00 58.30 34.30 32.20 7.80 4.9190 4.8280 0.19 0.19 0.20 8.10 3.80 64.03 5.50 8.20 0.10 0.47 0.40 0.90 0.16 28.10 31.03 7.77 0.90 55.28 0.17 0.73 3.07 0.70 0.67 1.94 2.6 1545.23 0.50 9.10 8.23 6.46 0.20 30.94 0.6 3.50 52.10 49.81 3.90 0.43 2.56 ao 2.14 0.60 1.10 0.00 0.53 0.53 0.70 8.10 8.30 49.4 1597.04 0.31 0.02 8.13 0.90 28.11 0.11 55.60 27.19 0.00 5.75 1.6400 1564 1546 1598 7.09 7.5099 1.7140 0.0369 3.4550 1.43 0. 23 0.54 %Ni %Al %Ti %Ca %Mg 0.28 0.23 0.022 0.27 0.045 0.019 0.016 0.0006 0.37 12 0.26 0.00003 0.52 Sample Before Alloying at Ladle Furnace station 1 0.186 0.175 0.27 0.23 0.028 0.03 0.019 0.029 0.0005 0.27 0.00016 0.27 5 0.21 0.016 0.22 0.10 0.026 0.245 0.00003 0.11 0.00003 0.61 0.00017 0.28 0.00003 0 0 0 0.180 0.52 12 0.044 0.042 0.015 0.00021 0.27 0.0004 0.29 0.19 0.033 0.45 9 0.04 0.08 0.00339 0.02 0.052 0.14 0.28 0.37 0.38 0.00003 0.00049 0.0002 0.14 0.17 0.012 0.18 0.00019 0.00017 0.016 0.27 0.0001 0.27 10 0.030 0.00005 0.28 0.026 0.12 0.26 0.32 0.01 0.08 0.068 0.00019 0.19 0.01 0.056 0.18 0.00003 0.00004 0.00292 0.024 0.014 0.08 0.08 0.02 0.020 0.014 0.41 2 0.26 0.25 0.023 0.32 0.0003 0.20 0.2 4 0.00018 0.19 0.0001 0.10 0.17 0.064 0.20 0.00003 0.014 0.09 0.013 0.36 3 0.07 0.13 0.16 0.13 0.004 0.00005 0.19 0.01 0.0003 0.22 0.18 0.00019 0.38 0.0003 0.43 6 0.0002 0.236 0.18 0.36 8 0.0003 0.03 0.016 0.48 11 0.20 0.00017 0.37 0.00003 0.18 4 0.00020 0.35 11 0.014 0.02 0.49 12 0.44 11 0.0004 0.09 0.28 0.024 0.60 0.062 0.022 0.20 0.32 0.42 Sample After Tapping 1 0.04 0.00018 0.012 0.198 0.105 0.26 0.00009 0.0004 0.011 0.00012 0.30 0.0003 0.10 0.21 0.00023 0.32 7 0.30 0.014 0.00011 0.11 0.277 0.012 0.24 0.0003 0.013 0.00019 0.24 10 0.00011 0.26 10 0.00016 0.0006 0.25 0.13 0.07 0.0003 0.07 0.00018 0.0001 0.004 0.00010 0.00004 Continue on the next page 52 .162 0.17 0.027 0.16 0.0002 0.0002 0.00 0.027 0.00006 0.00019 0.00006 0.0004 0.00005 0.00003 0.24 0.00012 0.028 0.0006 0.10 0.29 0.62 2 0.34 8 0.00006 0.00025 0.0003 0.00025 0.033 0.0005 0.0003 0.016 0.13 0.24 8 0.0002 0.10 0.18 0.13 0.00013 0.13 0.050 0.00045 0.00024 0.00006 0.25 0.25 0.30 0.76 0.06 0.44 6 0.0004 0.29 5 0 0 0 0 0 6 0.23 0.015 0.31 0.01 0.0005 0.00012 0.05 0.017 0.00003 0.19 4 0.36 3 0.14 0.014 0 0.18 0.28 0.04 0.29 0.Appendix II: Steel samples for all Heats Heat %C %Si %Mn %S %Cr Sample ein the EAF Before Tapping 1 0.00023 0.00005 0.00005 0.11 0.20 0.002 0.33 7 0.02 0.063 0.00016 0.25 0.27 0.00004 0.18 0.00016 0.24 0.27 0.024 0.18 0.00009 0.050 0.59 9 0.00031 0.29 5 0.00008 0.011 0.014 0.00017 0.00003 0.257 0.21 7 0.22 0.19 0.014 0.00003 0.10 0.00009 0.0006 0.065 0.13 0.10 0.04 0.00005 0.08 0.01 0.57 9 0.27 0.0003 0.04 0.62 2 0.13 0.09 0.23 0.017 0.02 0.00003 0.08 0.24 0.0003 0.20 0.00006 0.20 0.00037 0.215 0.00016 0.24 0.0003 0.10 0.00018 0.01 0.19 0.0005 0.26 3 0.017 0.13 0.20 0.00004 0.0004 0.04 0.20 0.0002 0. 13 0.034 0.00019 0.290 -0.016 0.71 1.97 0.0006 0.10 0.026 0.033 0.4 1.29 0.00033 Appendix III: Interaction Coefficients of activities of dissolved elements in steel (17) j C Si Mn P S Cr Mo Al j es 0.67 1.00009 0.037 0.13 0.00023 0.32 8 0.0014 0.0013 0.022 0.006 0.22 4 0.011 0.20 0.0003 0.053 0.028 0.15 0.29 10 0.34 0.016 -0.017 1.00023 0.013 0.28 0.007 0.00029 0.022 0.00019 0.001 0.013 0.041 0.13 0.7 1.12 0.0056 0.016 0.057 0.28 0.17 0.004 -0.55 0.030 0.027 0.0006 0.032 0.0006 0.0630 -0.037 0.25 0.000 0.52 1.27 0.44 2.15 0.25 1.65 9 0.081 0.72 0.28 Sample after Degassing 1 0.11 0.00029 0.97 0.00045 0.30 0.12 0.25 0.94 0.25 0.00031 0.00020 0.34 0.00029 0.48 0.31 2 0.03 1.013 0.14 0.95 0.00119 0.00023 0.00031 0.076 0.0000 0.00047 0.92 0.00020 0.0005 0.0013 0.0009 0.44 2.22 3.00013 0.00025 0.20 0.31 0.87 6 0.00025 0.47 1.00032 0.14 1.000 0.0009 0.00020 0.035 j e Al 0.00013 0.10 0.70 3 0.003 j 0.042 0.00011 0.00023 0.010 0.48 0.000 e Al 53 .14 0.003 0.34 0.15 7 0.044 0.71 1.008 0.25 1.007 0.00019 0.10 0.00025 0.67 11 0.0005 0.001 0.46 1.00021 0.00023 0.00018 0.93 0.96 0.29 12 0.00017 0.01 0.41 1.26 0.0009 0.0005 0.14 7 0.00018 0.081 0.7 1.11 0.45 2.029 0.006 0.0008 0.012 0.67 11 0.27 0.85 6 0.25 0.025 0.00020 0.02 1.0007 0.10 0.70 3 0.18 0.045 j Cu V Sn Ti W Ca Co j es -0.7 0.0014 0.000 0.00011 0.29 Final sample 1 0.08 0.0005 0.17 0.00023 0.15 0.90 0.00019 0.28 10 0.013 0.15 0.007 1.4 1.0013 0.13 0.20 1.22 0.001 0.00012 0.00024 0.030 0.10 0.22 3.001 0.001 0.18 0.091 0.00020 0.17 7 0.22 4 0.079 0.31 2 0.91 0.65 9 0.09 0.00022 0.22 3.67 1.00025 0.33 8 0.15 0.0009 0.00020 0.0007 0.13 0.25 1.00018 0.034 0.005 0.0003 0.00025 0.00022 0.00005 0.30 12 0.00024 0.13 0.001 0.20 1.68 1.29 0.022 0.98 0.68 1.15 0.65 11 0.93 0.0004 0.Heat %C %Si %Mn Sample Before Degassing 1 0.00009 0.056 0.00022 0.001 0.023 0.029 0.004 0.006 1.00029 0.00017 0.39 1.03 0.041 0.00022 0.011 0.00011 0.020 0.50 0.00020 0.11 0.19 1.051 0.65 0.10 0.62 3 0.00024 0.7 0.14 0.00027 0.15 0.34 0.48 0.21 0.00027 0.47 1.17 0.0014 0.42 1.42 1.144 0.22 0.010 0.013 0.22 4 0.0013 0.93 0.072 0.65 9 0.013 0.67 1.0013 0.08 0.17 0.14 0.27 0.026 0.00021 0.000 0.92 0.025 0.0004 0.0011 0.30 0.00019 0.033 0.18 0.52 1.0008 -0.66 0.0005 0.028 -0.51 1.000 0.31 10 0.08 0.036 0.047 0.00017 0.00033 0.14 0.29 0.94 0.36 0.31 0.20 5 0.28 0.32 8 0.0005 0.30 12 0.048 0.052 0.0014 0.00255 0.03 1.00 -0.30 2 0.97 0.110 0.11 0.044 0.76 0.99 0.0005 0.28 0.00020 0.010 0.000 0.42 0.057 0.00016 0.000 0.21 5 0.00019 0.00020 0.00038 0.045 0.00020 0.00027 0.13 0.22 0.18 5 0.043 0.0013 0.045 0.22 0.0005 0.00017 0.20 1.040 0.26 0.17 0.000 0.22 1.00024 0.011 0.31 0.00020 0.020 0.057 0.30 %S %Cr %Ni %Al %Ti %Ca %Mg 0.87 6 0. Appendix IV: Variation of SiO2 content of slag 25 1-Sample in EAF b efore Tapping 2-Sample at tapping 3-Sample b efore slag removal 4-Synthetic slag 5-Sample b efore degasing 6-Sample after Degassing 7-Sample at completion of refining 20 %SiO2 15 10 5 0 0 1 2 3 4 Process Stage 5 6 7 Heat 1 Heat 2 Heat 3 Heat 4 Heat 5 Heat 6 Heat 7 Heat 8 Heat 9 Heat 10 Heat 11 Heat 12 8 Appendix V: Variation of MnO content of slag 8 1-Sample in EAF before Tapping 2-Sample at tapping 3-Sample b efore slag removal 4-Synthetic slag 5-Sample b efore degasing 6-Sample after Degassing 7-Sample at completion of refining 7 6 %MnO 5 4 3 2 1 0 0 1 2 3 4 Process Stage 5 6 7 Heat 1 Heat 2 Heat 3 Heat 4 Heat 5 Heat 6 Heat 7 Heat 8 Heat 9 Heat 10 Heat 11 Heat 12 8 54 . Appendix VI: Variation of CaO content of slag 80 70 60 %CaO 50 40 30 1-Sample in EAF b efore Tapping 2-Sample at tapping 3-Sample b efore slag removal 4-Synthetic slag 5-Sample b efore degasing 6-Sample after Degassing 7-Sample at completion of refining 20 10 0 0 1 2 3 4 Process Stage 5 6 7 Heat 1 Heat 2 Heat 3 Heat 4 Heat 5 Heat 6 Heat 7 Heat 8 Heat 9 Heat 10 Heat 11 Heat 12 8 Appendix VII: Variation of Al2O3 content of slag 40 35 30 %Al 2O3 25 20 15 1-Sample in EAF b efore Tapping 2-Sample at tapping 3-Sample b efore slag removal 4-Synthetic slag 5-Sample b efore degasing 6-Sample after Degassing 7-Sample at completion of refining 10 5 0 0 1 2 3 4 5 6 7 8 Process Stage Heat 1 Heat 2 Heat 3 Heat 4 Heat 5 Heat 6 Heat 7 Heat 8 Heat 9 Heat 10 Heat 11 Heat 12 55 . Appendix VIII: Variation of MgO content of slag 30 1-Sample in EAF b efore Tapping 2-Sample at tapping 3-Sample b efore slag removal 4-Synthetic slag 5-Sample b efore degasing 6-Sample after Degassing 7-Sample at completion of refining 25 %MgO 20 15 10 5 0 0 1 2 3 4 Process Stage 5 6 7 Heat 1 Heat 2 Heat 3 Heat 4 Heat 5 Heat 6 Heat 7 Heat 8 Heat 9 Heat 10 Heat 11 Heat 12 8 Appendix IX: Variation of FeO content of slag 25 1-Sample in EAF b efore Tapping 2-Sample at tapping 3-Sample b efore slag removal 4-Synthetic slag 5-Sample b efore degasing 6-Sample after Degassing 7-Sample at completion of refining %FeO 20 15 10 5 0 0 1 2 3 4 Process Stage 5 6 7 Heat 1 Heat 2 Heat 3 Heat 4 Heat 5 Heat 6 Heat 7 Heat 8 Heat 9 Heat 10 Heat 11 Heat 12 8 56 . 4288 TiO2 0.0000 0.006 0.10 0.37 Mass of Top slag = Mass of CaO in sythetic slag / % Cao before degassing = 931.26 0.'Amt Before' .23 457.77 22.45 6.65 -2.30 264.1700 1.00 8.90 -1.00 1.39 -3.00013 0.00000 0.00 Steel analysis during casting [%] 0.09 -0.43 26.00 0.'Alloy addition') [kg] Slaganalysis before degassing [%] Weight before degassing [kg] Extra slag addition [kg] Slag analysis after degassing [%] Weight after degassing [kg] Mass difference in slag [kg] Equivalent element in slag [kg] Elemental Sum in slag&steel Final sample Si 0.00 28.37 -2.03 Mg 0.04 31.30 0.70 81.5897 0.05 0.77 1.77 MnO 0.65 S 0.65 60.90 36.00 0.45 0.51 0.70 62.36 0.20 11.34 0.0002 Al 0.19 1.84 -10.14800 0.45 9.07 0.34 527.2268 0.10 -16.00 0.01 -12.00 0.36 -4.00 0.02 -3.34 -8.14Kg Extraslag=Mass of Topslag after degassing .'Alloy addition') [kg] -7.25 3.00 -20.19 1.0003 0.0003 0.42 0.05 Mg 0.37 0.01964 MgO 6.1890 CaO 66.08 7.01 Ti 0.66 MnO 1.00 0.34 31.00 0.00 0.18 22.07 23.67 29.42 S 0.26 0.00004 0.23 Mass of Top slag = Mass of CaO before degassing / % Cao after degassing = 935.73 0.41 TiO2 0.2114 0.60 527.39 -24.0000 0.1127 0.67 0.49 MgO 4.18 0.00029 0.05 0.96 -31.00 0.67 -23.Mass of synthetic slag = 136.10 57.42 56.'Amt Before' .0150 -15.029 0.6556 0.42 0.Mass of Topslag before degassing=3.25 FeO 3.10 0.00032 Mass diff (Final mass .05 9.70 180.6184 0.Appendix X: Mass Balance of Heat 12 Heating and Alloying Analysis before alloying [%] Alloying [kg] Sample before degassing [%] Si 0.25 -3.03 36.0009 0.70 62.0103 -3.25 0.1300 1.00 0.0013 Ca 0.00013 Mass difference ('amt after' .00 0.3153 0.032 0.84Kg Extra slag = Mass of Top slag before degassing .2114 0.42 0.18 10.25 Mn 0.90 204.84kg Degassing Steelanalysis before degassing[%] Extra alloying [kg] Steel analysis after degassing [%] Mass difference ('amt after' .42 0.005 0.1300 1.02 16.52 23.10 1.8074 0.14 1.67 S 0.0000 0.0009 Ca 0.20 85.00 Al2O3 22.01 4.59 12.74 0.66 5.00 0.09 0.Initial mass[kg]) 0.26 Mn 0.32 0.97 0.3784 0.77 0.49 21.0002 Al 0.30kg Si Mn S Ti Ca Al Mg Steel analysis after degassing [%] Extra alloying [kg] 0.73 63.41 1.46 35.57 32.00029 14.0000 0.65 0.81 S 0.0002 0.8961 0.73 0.07 0.25 14.43 0.94 0.82 Al2O3 21.00 0.60 527.90 36.99 16.00 0.09262 Synthetic slag [%] Weight of synthetic slag [kg] Slaganalysis before degassing[%] Weight before degassing [kg] Mass difference in slag [kg] Equivalent element in slag [kg] SiO2 2.27 Elemental Sum in slag&steel [Kg] FeO 0.53 4.0549 CaO 56.0000 0.0013 0.20 11.56 SiO2 9.0013 0.90 204.40 527.22 9.00 6.10 24.20 11.67 0.0002 0.0000 0.01 Ti 0.20 85.03102 57 .05 11.04 -5.40 12.02 0.00 56.0002 0.09 0. 67E-05 6.61E-04 2.61E-04 2.91E-04 2.29E-04 2.14E-04 2.89E-04 2.05E-04 3.93E-04 1.002-0.33E-05 1.44E-04 2.04E-04 3.1 1500 1550 1600 1650 1700 1750 Temp (C) 0.020-0.22E-04 3.64E-04 1.64E-05 Al2O3 =1 2.86E-05 3.85E-04 ao 2.019 0.050-0.13E-04 58 .26E-04 Data 2.84E-04 1.82E-04 4.32E-04 2.58E-04 1.56E-05 4.53E-04 3.28E-04 4.07E-05 1.06E-05 1.85E-05 3.Appendix XI: Model for predicting ao activity for online process using existing process data 1000 ao (ppm) 100 10 1 0.030 0.41E-04 1.17E-05 2.008-0.90E-04 2.031-0.12E-04 3.65E-05 3.46E-04 3.004%Al 0.84E-04 2.40E-04 2.59E-04 5.049 0.95E-04 2.94E-04 1.03E-04 3.84E-05 4.75E-04 2.59E-04 3. Appendix XII: Comparison of Different Models of estimating ao Measured Calculated Heats 1 2 3 4 5 6 7 8 9 10 11 12 Ohta&suito 2.16E-06 1.069 .069 >0.34E-04 2.16E-04 1.00E-04 2. 30E-04 1.85E-04 2.12E-04 3.10E-04 3.80E-04 3.52E-04 2.78E-04 2.86E-04 4.14E-04 2.61E-04 2.73E-04 ao 2.82E-04 4.97E-04 3.65E-05 2.69E-04 5.03E-04 3.40E-04 Al2O3=1 2.94E-04 3.70E-04 1.70E-04 3.55E-04 1.25E-04 1.53E-04 3.59E-04 5.25E-04 2.76E-04 2.89E-04 3.59E-04 2.19E-04 5. ao 426 111 1434 885 275 218 690 220 1297 383 478 338 Ls 130 48 970 750 121 185 118 186 188 240 91 300 59 .95E-04 3.94E-04 3.13E-04 Appendix xiii: Calculated and Measured Equilibrium Sulphur distribution Calculated Ls Heats 1 2 3 4 5 6 7 8 9 10 11 12 Ohta&suito 4498 671 71815 10917 3890 1818 14948 3424 25155 3207 5893 2901 Al2O3=1 517 156 1161 1030 348 263 810 373 1711 505 666 324 Measured Meas.69E-04 3.39E-04 3.22E-04 3.88E-04 3.21E-04 3.52E-04 5.76E-04 9.85E-04 3.41E-04 1.43E-04 2.88E-04 1.36E-04 2.71E-04 1.18E-04 Measured Data 3.04E-04 3.40E-04 2.Appendix XIII: Modified oxygen activities Calculated Heats 1 2 3 4 5 6 7 8 9 10 11 12 Ohta&suito 2. 019 0.001 0.003 0.005 0.005 0.015 0.020 0.007 60 .006 0.001 0.001 0.010 0.Appendix xiv: Equilibrium Sulphur content in steel Calculataed Heat 1 2 3 4 5 6 7 8 9 10 11 12 Ohta&suito 0.010 0.001 0.006 [%S]f 0.008 0.014 0.005 0.001 0.005 0.003 0.004 0.006 Al2O3=1 0.003 0.012 0.016 0.001 0.004 0.013 0.005 0.001 0.001 0.002 0.001 0.001 0.014 0.003 0.003 0.001 0.012 0.007 Measured Meas ao 0.006 0.004 0.003 0.009 0.018 0.005 0.023 0.