This work investigates the interactions of carbonaceous materials (metallurgical coke, natural graphite and HDPE/coke blends) with three EAF slags [FeO: 24% to 32%]. Experiments were conducted using the sessile drop technique (1500??C-1600??C) with off-gases (CO, CO2) measured using an IR analyzer; the wetting behaviour was determined from contact angle measurements. Estimation of slag foaming behaviour was determined from the droplet volume changes calculated using specialized software. At 1550??C, all slags were non-wetting with coke due to increased surface tension due to sulphur. At 1550??C, slag 1 was initially non-wetting on natural graphite due to gas entrapment in the slag droplet; the wetting improved after that. Other slags showed comparatively better wetting. At 1600??C, all slags were non-wetting with coke. Slags showed a shift from non-wetting to wetting behaviour with natural graphite. Slag/coke reactions produced high off-gases levels causing extensive FeO reduction; gas entrapment in the slag was poor (small volume droplets). Slag/natural graphite interactions revealed both slow gas generation rates and FeO reduction, and excellent gas entrapment (higher droplet volumes) with minor changes in slag properties due to low ash levels. The iron oxide reduction rates were determined to be 1.54x10-5 and 4.2x10-6 mol.cm-2/sec (Slag 1, 1550??C) for metallurgical coke and natural graphite respectively. Slag interactions with coke/HDPE blends showed increasing off-gas levels with increasing HDPE levels. Blend#3 produced the highest off-gas levels, extensive FeO reduction and displayed significantly higher slag foaming and better wetting compared to coke. Our line on trends compared well for slag/carbon interactions and resulted in deceased specific energy consumption and carbon usage and increased productivity. These findings have enhanced the possibility of utilizing polymeric wastes in blends with coke in EAF steelmaking for slag/carbon interactions.

This work investigates the interactions of carbonaceous materials (metallurgical coke, natural graphite and HDPE/coke blends) with three EAF slags [FeO: 24% to 32%]. Experiments were conducted using the sessile drop technique (1500??C-1600??C) with off-gases (CO, CO2) measured using an IR analyzer; the wetting behaviour was determined from contact angle measurements. Estimation of slag foaming behaviour was determined from the droplet volume changes calculated using specialized software. At 1550??C, all slags were non-wetting with coke due to increased surface tension due to sulphur. At 1550??C, slag 1 was initially non-wetting on natural graphite due to gas entrapment in the slag droplet; the wetting improved after that. Other slags showed comparatively better wetting. At 1600??C, all slags were non-wetting with coke. Slags showed a shift from non-wetting to wetting behaviour with natural graphite. Slag/coke reactions produced high off-gases levels causing extensive FeO reduction; gas entrapment in the slag was poor (small volume droplets). Slag/natural graphite interactions revealed both slow gas generation rates and FeO reduction, and excellent gas entrapment (higher droplet volumes) with minor changes in slag properties due to low ash levels. The iron oxide reduction rates were determined to be 1.54x10-5 and 4.2x10-6 mol.cm-2/sec (Slag 1, 1550??C) for metallurgical coke and natural graphite respectively. Slag interactions with coke/HDPE blends showed increasing off-gas levels with increasing HDPE levels. Blend#3 produced the highest off-gas levels, extensive FeO reduction and displayed significantly higher slag foaming and better wetting compared to coke. Our line on trends compared well for slag/carbon interactions and resulted in deceased specific energy consumption and carbon usage and increased productivity. These findings have enhanced the possibility of utilizing polymeric wastes in blends with coke in EAF steelmaking for slag/carbon interactions.

<p>Recent experiment in our laboratory demonstrates that an increase in slag foamingwith carbon injection rate is limited by slag volume. The current work has identified arelationship between foam height, carbon injection rate and slag volumes, whichpredicts the critical injection rate above which foaming become inefficient. Theprediction of critical injection rate employs an extension of understanding mechanismof bubble movement in the foam by estimating average/steady-state bubble size andwall thickness. The carbon gasification model developed in our laboratory by King etal., which has been extended to include greater consideration of gas bubble burstingwhen to predict bubble size, and further improvement for calculating how fast bubblecan burst instantaneously in carbon-gas-slag halo system, has found that has importantinfluence on the predicting foaming parameters in King’s model, which is crucial taskfor continuous development in future.</p> / Master of Applied Science (MASc)

The present thesis deals with the development of a new type of dynamic model for metallurgical reactors. It also covers some of the theoretical aspects of steelmaking that is necessary to include in such an application. The thesis consists of modeling work, high temperature experiments and cold model experiments. Two different aspects of slags in the oxygen steelmaking were investigated. In the first study, slag samples were equilibrated with copper at 1923K in order to study their capacities in capturing phosphorous. Some of the samples were liquid-solid mixtures. The solid phases in these samples were identified by SEM analysis. The identified phases were found to agree well with Thermocalc calculations while the amount of solid fractions didn’t. The phosphorous distribution between the different phases was examined. The phosphate capacities of the samples were evaluated. The MgO content didn’t show any appreciable impact on the phosphate capacity. Furthermore the activities of FeO in the liquid slag samples were calculated and were found to deviate positively from ideality. In the second study the foaming height of CaO-SiO2-FeO slags by the reaction with hot metal was investigated. It was found that the foaming height increased with increasing FeO content up to 20-25%. The foaming height was seen to decrease with increased viscosity. The present results indicated that simply using foaming index for converter slag might lead to wrong conclusion. Simulation experiments using cold model at room temperature were conducted. Cold model experiments were carried out in order to study the penetration depth due to an impinging gas jet on the surface of a liquid metal. The liquid alloy Ga-In-Sn was used to simulate steel. And an HCl solution was used to simulate the slag. A comparison with predictions of existing models was made and a new model parameter was suggested. The observation of the movement of metal droplets generated by the gas jet was also made. The low velocity of droplets suggested that the turbulent viscosity played important role and the droplets could have long resident time in the slag. Furthermore a study of the effect of gas flow rate on homogenization and inclusion removal in a gas stirred ladle was carried out. Both industrial trials and cold model experiments were conducted. As an auxiliary tool CFD was used to predict the mixing times and was found to agree well with both the model experiments and industrial data. The increase of flow rate of inert gas would not improve the mixing substantially at higher flow rates. The water model study showed also that the gas flow rate had negligible effect on the rate of inclusion removal. Both the experiments and CFD calculation strongly suggested that low gas flow rate should be applied in the ladle treatment. Lastly a new approach to a dynamic process model of 300 ton BOF converter was made. The main feature was to utilize the velocity vectors obtained by CFD simulation. In the standalone model, the steel melt domain was sliced into 1000 cells. Based on the imported velocity vectors from the CFD calculation, the mass transfer of carbon and phosphorus was calculated taking into account the slag metal reactions. The mass exchange between slag and metal was considered to be dominated by the metal droplet formation due to oxygen jet. The convergence of the model calculation and the promising comparison between the model prediction and the industrial data strongly suggested that the proposed approach would be a powerful tool in dynamic process control. However, more precise descriptions of other process aspects need to be included before the model can be practically employed in a dynamic controlling system. / <p>QC 20120829</p>

The objective of the present thesis is to optimize the electric arc furnace (EAF) practice from an environmental view point. Two aspects that meet the requirements of the secondary steelmaking industries today, viz. Mo alloying with maximum retainment of the alloying element in molten steel and optimization of foaming by carbonate addition with a view to optimize the energy need of the process. Both these aspects would also have a significant impact on the process economy. Iron molybdate (Fe2MoO4) has been synthesized from commercial grade materials and proposed as a new potential precursor for steel alloying with Mo. The thermal stabilities of different molybdates, viz. Fe2MoO4, CaMoO4 and MgMoO4, were studied using thermogravimetry analysis (TGA). It was found that Fe2MoO4 is the most stable one and doesn’t evaporate in Ar atmosphere when heating up to 1573 K. The synthesis of Fe2MoO4 requires high temperature (1373 K) and long holding time (up to 16 hours). In a view of this, the possibilities for in-situ formation of Fe2MoO4 and CaMoO4 from their precursor mixtures were studied with the aid of high-temperature X-ray diffraction (XRD) and TGA analysis. Laboratory and industrial trials on steel alloying with Mo were conducted using precursor mixtures as sources of Mo. It was found that the mixture, which contains FeOx, MoO3 and C (Fe2MoO4 precursor), can provide the Mo yield up to 98 % at both the laboratory as well as industrial trials. The Mo yields even in the case of C+MoO3 and C+MoO3+CaO mixtures were around 93 % in these trials. The higher yield for the MoO3+C+FeOx mixture was attributed to the stabilization of Mo in the precursor (marked by the decrease in the Gibbs energy of Mo) and the readiness to dissolve in the steel bath. The heat effect of the slag foaming with carbonates addition was studied at 1623 and 1673 K with the aid of thermal analysis technique with a new crucible design. Experiments were conducted by adding limestone and dolomite pieces of defined shapes (together with iron sinkers) in molten slag and monitoring the temperature changes accompanying the decomposition of carbonates. It was found that the decomposition energies for dolomite and limestone for the studied slag composition are in the range 56-79 % of theoretical values, which is linked to the energy saving effect of slag foaming. No influence of sample shape on decomposition energy was found both for limestone and dolomite. The kinetics of slag foaming by limestone particles was studied at 1773 K with the aid of X-ray imaging system. A model was proposed to describe the decrease in foam height with time on the basis of CaO shell formation during decomposition reaction. The energy impact of limestone and raw dolomite addition was examined in a 100-ton EAF. It was found that, in the case of addition of carbonates after the scrap is completely molten; the endothermic heat effects for limestone and dolomite (2255 and 2264 kJ/kg respectively) were only 70 % from theoretical values. This is indicative of the resistance to heat transfer due to increased foaming. / QC 20100914

<p>Electric arc furnace (EAF) is a furnace that utilizes electric energy and chemical energy to melt scraps and produce liquid steel. During the industrial process of EAF, an electric arc will be generated around the electrode located at the center of the furnace, and this phenomenon will generate a lot of heat. If any part of the electric arc is exposed to the freeboard region, a region above the slag layer inside the furnace, the heat emitted by this exposed arc can significantly heat on side wall temperatures, resulting in an overheating issue of side wall. Water-cooling panels (WCP) have been used to cool down the side wall, but the concentrated overheating area, may damage the water-cooling panel. In this study, a combination of slag foaming phenomenon and electric arc has been considered. A calculator is developed based on several arc models to calculate the parameters about slag foaming and arc power. The parameters can be used as input in a computational fluid dynamics (CFD) model. The commercial software, ANSYS FLUENT^®, was utilized to give a prediction of the side wall temperature distribution of an EAF. Data from the plant has been used to validate the calculation results. Furthermore, a series of parametric studies has been investigated to study the influence of operating conditions. The developed model can help to predict the risk of overheating from given electrode conditions and slag compositions.</p>

<p>The high temperature microstructure of the solid phases within the electric arc furnace (EAF) slag has a large effect on the process features such as foamability of the slag, chromium recovery, consumption of the ferroalloys and the wear rate of the refractory. The knowledge of the microstructural and compositional evolution of the slag phases during the EAF process stages is necessary for a good slag praxis.</p><p>In <strong>supplement 1</strong>, an investigation of the typical characteristics of EAF slags in the production of the AISI 304L stainless steel was carried out. In addition, compositional and microstructural evolution of the slag during the different EAF process stages was also investigated. Computational thermodynamics was also used as a tool to predict the equilibrium phases in the top slag as well as the amount of these phases at the process temperatures. Furthermore, the influence of different parameters (MgO wt%, Cr₂O₃ wt%, temperature and the top slag basicity) on the amount of the spinel phase in the slag was studied. In <strong>supplement 2</strong>, a novel study to characterize the electric arc furnace (EAF) slags in the production of duplex stainless steel at the process temperatures was performed. The investigation was focused on determining the microstructural and compositional evolution of the EAF slag during and at the end of the refining period.</p><p>Slag samples were collected from 14 heats of AISI 304L steel (2 slag samples per heat) and 7 heats of duplex steel (3 slags sample per heat). Simultaneously with each slag sampling, the temperature of the slag was measured. The selected slag samples were studied both using SEM-EDS and LOM. In some cases (<strong>supplement 2</strong>), X-ray diffraction (XRD) analyses were also performed on fine-powdered samples to confirm the existence of the observed phases.</p><p>It was observed that at the process temperature and at all process stages, the stainless steel EAF slag consists mainly of liquid oxides, magnesiochromite spinel particles and metallic droplets. Under normal operation and at the final stages of the EAF, 304L steelmaking slag contains 2-6 wt% magnesiochromite spinel crystals. It was also found that, within the compositional range of the slag samples, the only critical parameter affecting the amount of solid spinel particles in the slag is the chromium oxide content. Petrographical investigation of the EAF duplex stainless steelmaking showed that, before FeSi-addition, the slag samples contain large amounts of undissolved particles and the apparent viscosity of the slag is higher, relative to the subsequent stages. In this stage, the slag also includes solid stoichiometric calcium chromite. It was also found that, after FeSi-injection into the EAF and during the refining period, the composition and the basicity of the slag in the EAF duplex steelmaking and EAF stainless steelmaking are fairly similar. This indicates that, during the refining period, the basic condition for the utilization of an EAF foaming-slag praxis, in both austenitic and duplex stainless steel cases, is the same. Depending on the slag basicity, the slag may contain perovskite and/or dicalcium silicate too. More specifically, the duplex stainless steel slag samples with a higher basicity than 1.55 found to contain perovskite crystals.</p>

In the steel industry, slag foaming plays a crucial role in many steel processes, given its positive impact on the thermal efficiency of the furnace and its life span. However, excessive foaming causes an overflow in the converter known as “slopping”. Slopping hinders the effectiveness of the processes, especially with the complex and unpredictable foaming rate. This problem occurs mainly in the BOS-processes and after melt tapping to the ladle furnace. The goal of this study is to test and relate a new foaming control system, by blowing a gas (nitrogen or argon) on the surface of the melt to suppress the foam. Firstly, the foaming index of the provided industrial heats for a general LD converter (21 heats) and Outokumpu’s ladle furnace (31 heats) were calculated to find which heat is most likely to slop. Then, a series of experiments were performed to investigate the new foam controlling system’s reliability using a cold model. The results demonstrated that blowing argon instead of nitrogen from the top nozzle suppresses the foam more effectively, which can be attributed to its higher density. Additionally, the optimal argon flow rate required to suppress the foam in worst-case slopping scenarios in the LD converter and the ladle furnace were 874 and 221 m3/min respectively. The provided data further supports the efficacy of this slopping prevention technique, in theoretical and practical aspects. / I stålindustrin spelar slaggskumning en avgörande roll i många stålprocesser, med tanke på dess positiva inverkan på ugnens termiska effektivitet och dess livslängd. Överdriven skumning orsakar emellertid ett överflöde i konvertern som kallas "utkok". Utkok hindrar processernas effektivitet, särskilt med den komplexa och oförutsägbara skumningshastigheten. Detta problem uppstår främst i BOS-processerna och efter tappning till skänkugnen. Målet med denna studie är att testa ett nytt kontrollsystem genom att blåsa en gas (kväve eller argon) på smältytan för att slå sönder skummet. Först beräknades skumindexet för de tillhandahållna industriella chargerna för en allmän LD (21 charger) och Avestas skänk (31 charger) för att hitta vilken charge som har störst risk för utkok. Därefter utfördes en serie experiment för att undersöka det nya skumstyrsystemets tillförlitlighet med hjälp av en kall modell. Resultaten visade att blåsning av argon istället för kväve från det övre munstycket undertrycker skummet mer effektivt, vilket kan hänföras till dess högre densitet. Dessutom var den optimala argonflödeshastigheten som krävdes för att undertrycka skummet i värsta fallet i LD och skänkanläggningen 871 respektive 221 m3/min. De tillhandahållna uppgifterna stöder ytterligare effekten av denna förebyggande teknik, i teoretiska och praktiska aspekter.

The high temperature microstructure of the solid phases within the electric arc furnace (EAF) slag has a large effect on the process features such as foamability of the slag, chromium recovery, consumption of the ferroalloys and the wear rate of the refractory. The knowledge of the microstructural and compositional evolution of the slag phases during the EAF process stages is necessary for a good slag praxis. In supplement 1, an investigation of the typical characteristics of EAF slags in the production of the AISI 304L stainless steel was carried out. In addition, compositional and microstructural evolution of the slag during the different EAF process stages was also investigated. Computational thermodynamics was also used as a tool to predict the equilibrium phases in the top slag as well as the amount of these phases at the process temperatures. Furthermore, the influence of different parameters (MgO wt%, Cr2O3 wt%, temperature and the top slag basicity) on the amount of the spinel phase in the slag was studied. In supplement 2, a novel study to characterize the electric arc furnace (EAF) slags in the production of duplex stainless steel at the process temperatures was performed. The investigation was focused on determining the microstructural and compositional evolution of the EAF slag during and at the end of the refining period. Slag samples were collected from 14 heats of AISI 304L steel (2 slag samples per heat) and 7 heats of duplex steel (3 slags sample per heat). Simultaneously with each slag sampling, the temperature of the slag was measured. The selected slag samples were studied both using SEM-EDS and LOM. In some cases (supplement 2), X-ray diffraction (XRD) analyses were also performed on fine-powdered samples to confirm the existence of the observed phases. It was observed that at the process temperature and at all process stages, the stainless steel EAF slag consists mainly of liquid oxides, magnesiochromite spinel particles and metallic droplets. Under normal operation and at the final stages of the EAF, 304L steelmaking slag contains 2-6 wt% magnesiochromite spinel crystals. It was also found that, within the compositional range of the slag samples, the only critical parameter affecting the amount of solid spinel particles in the slag is the chromium oxide content. Petrographical investigation of the EAF duplex stainless steelmaking showed that, before FeSi-addition, the slag samples contain large amounts of undissolved particles and the apparent viscosity of the slag is higher, relative to the subsequent stages. In this stage, the slag also includes solid stoichiometric calcium chromite. It was also found that, after FeSi-injection into the EAF and during the refining period, the composition and the basicity of the slag in the EAF duplex steelmaking and EAF stainless steelmaking are fairly similar. This indicates that, during the refining period, the basic condition for the utilization of an EAF foaming-slag praxis, in both austenitic and duplex stainless steel cases, is the same. Depending on the slag basicity, the slag may contain perovskite and/or dicalcium silicate too. More specifically, the duplex stainless steel slag samples with a higher basicity than 1.55 found to contain perovskite crystals. / QC 20110413

Today, a huge part of waste products from pulp and paper industries ends up in landfill which is both economically and environmentally adversely. This report examines the possibilities of using those products as a slag foamer and fuel in different furnaces in the metal industry. The waste products contain valuable elements, especially carbon. Therefore, there is an increased interest in finding possible use for the waste products in the metal industry. The reuse would contribute to preservation of energy as fossil fuel can be replaced. In the report, two waste materials called mixed biosludge and fiber reject are examined. The experiments are performed with the waste products pressed together with a base material and cement forming a briquette. The requirements examined are strength needed for both transportation and use in furnaces and ability to create a foaming slag. The results in strength were ambiguous, no waste material based briquettes met the set criteria. As of now, the briquettes are probably not strong enough to be transported. No foaming occurred during the experiment, but only one experiment was performed. Therefore, further experiments are needed before any conclusions can be drawn. The briquettes can possibly replace coke and coal in applications where strength is not as important. Nevertheless, it is uncertain if the briquettes affect the steel quality. / Idag läggs en stor del av restprodukter från pappers och massaindustrin på deponi, vilket innebär såväl ekonomiska som miljömässiga nackdelar. Den här rapporten undersöker möjligheterna att använda dessa restprodukter som slaggskummare och bränsle i de olika ugnarna inom metallindustrin. Restprodukterna innehåller värdefulla ämnen, framförallt kol. Därför finns det ett ökat intresse för att hitta möjliga användningsområden för restprodukterna inom metallindustrin. Denna återanvändning skulle bidra till energibevarande eftersom fossila bränslen kan ersättas. I den här rapporten undersöks två restmaterial, blandat biologiskt slam och fiberavfall. Experimenten utfördes med dessa restprodukter pressade samman med ett basmaterial och cement till en brikett. Kraven som undersöks är styrka för både transport och användning i ugnarna samt förmågan att skumma en slagg. Resultaten för briketternas styrka var tvetydiga, inga av briketterna innehållande restprodukter satisfierade det uppsatta kriteriet. Styrkan är troligtvis för låg för att transport ska vara möjlig. Ingen skumning skedde under experimentet, men endast ett experiment genomfördes. Därför behöver ytterligare experiment genomföras innan några slutsatser kan dras. Men briketterna tros kunna ersätta koks och kol där styrkan inte är viktig. Men det är osäkert om briketterna påverkar stålkvaliteten.