Slag Foaming Research Articles

Microstructure, Mineral Phases and Strength of the Foam Concrete

The relationship among the composition, microstructure and strength of materials is always one of the hotspots for scholars of materials research. The influence of curing time on the compressive strength and flexural strength of the foam concrete with the cement, cement-slag and cement-steel slag as main binder respectively was studied in this paper. The microstructure of these foam concrete was analyzed by SEM and the mineral phases of the foam concrete was analyzed by XRD. The relationship among the binders, microstructure, mineral phases and strength of the foam concrete were explored and the reasons of why the strength of the cement foam concrete and cement-slag foam concrete is much higher than that of the cement-steel slag foam concrete are proposed.

Influence of direct reduced iron on the energy balance of the electric arc furnace in steel industry

A model of the EAF energy efficiency was developed based on a closed mass and energy balance of the EAF melting process. This model was applied to industrial EAFs in steel industry charged with scrap or with mixes of scrap and DRI. Complex mass and energy conversion in the EAF was simplified with the introduction of mass and energy conversion efficiencies for the conversion of oxygen and the energy conversion of electrical energy in the electric arcs, chemical energy from the oxidation reactions in the melt and energy from the combustion of burner gas. It turned out that close agreement with observed process parameters from 16 EAFs is obtained by slight variations of the efficiency values. Especially the sensitivity of the steel temperature from the energy conversion efficiency of the electric arc energy indicates the importance of efficient foaming slag operation in EAF steel making. Characteristics and process parameters of DRI charged EAFs are discussed. Model results for a series of case studies illustrate the correlations between DRI chemical composition, DRI portion, oxygen consumption, etc. with electrical energy demand in order to indentify cost-effective EAF process conditions.

Thermodynamic simulations and isothermal solubility diagrams as tools for slag foaming control

In this communication, the advantages and difficulties of the slag foaming process control are presented, highlighting the thermodynamic simulations role in the design of isothermal solubility diagrams (which express the relationship between MgO and FeO contents, in weight percentage, for a specific basicity and temperature). These diagrams can predict the liquid composition changes required in order to induce a longer foam lifetime at the upper surface of molten slags. Mathematical models and experimental tests have been used to understand the slag foaming phenomenon, however they do not simultaneously consider all variables involved in this process. Thus, a comparison between some experimental results and isothermal solubility diagrams was made in this work. According to this evaluation, the use of thermodynamic simulations can be a good alternative to help keeping the slag foam generation while some equipment is being used in the steel production. The use of isothermal solubility diagrams provides a clear image of which adjustments can be made in order to attain stable foam, reducing the needs for some additional experimental analyses.

Comparison Between Vessel Vibration and Audiometry for Slopping Control in the Top‐Blown BOS Process

AbstractExcess slag foam growth is a frequent problem in the BOS process. In the worst case, foam is forced out of the vessel and this phenomenon, commonly called slopping, not only results in loss of valuable metal yield but also in equipment damage and lost production time. In order to minimize slopping, accurate estimation of the foam level inside the vessel is an important part of BOS process control. In the top blown BOS vessel, slopping control is achieved using both static and dynamic measures. The most common implemented technique for dynamic foam height estimation and slopping control is the audiometer system. An alternative method, vessel vibration monitoring, has been investigated as part of the work in a RFCS funded research project called IMPHOS. In order to judge the usefulness of this method, parallel vibration and audio measurements have been carried out on 130 tonne as well as on 300 tonne BOS vessels. The results show that during stable process conditions there is good agreement between the two methods with regard to foam height estimation and, as vessel vibration and audiometry are largely independent of each other, a combination of the two is likely to increase significantly the accuracy of slopping prediction.

Ilmenite Smelted by Oxygen-Enriched Top-Blown Smelting Reduction

Total ilmenite from Yunnan, China, difficult to smelt in blast furnace, was smelted by oxygen-enriched top-blown smelting reduction ironmaking technology. Much more details on smelting were discussed. Specifically, the influence of reduction temperature, slag basicity and molar ratio of carbon to oxygen on the reduction quality level including iron recovery and titanium and sulfur contents in the pig iron produced in the experiment was investigated. Iron recovery rate could reach 95% with titanium content below 0. 05% in pig iron produced, under the conditions of holding time of 30 min at 1 823 K, basicity of 1.1, carbon to oxygen molar ratio of 1. 0 and oxygen-enriched flow rate of 250 L/h. Oxidization potential of top-space of smelting reduction vessel and slag combination could create the driving force to partition phosphorous, titanium and silicon into the slag, which ensured low contents of the impurities involved above and carbon in pig iron. In addition, it avoided the generation of Ti(C, N) that could reduce interfacial tension of slag, which induced the formation of foaming slag seriously. Furthermore, jam of chargings and bubble flooding would be triggered, resulting in deterioration of BF state, increase of iron loss and decline of desulfurization rate.

The Effect of Solid Particles on Liquid Viscosity

AbstractThe viscosities of solid‐liquid mixtures were experimentally determined for silicon oil‐paraffin system at room temperature and solid‐liquid oxide mixture at steelmaking temperature. The use of oil‐paraffin systems was to confirm the results of high temperature measurements, the experimental conditions being very difficult to control. The silicon oil‐ paraffin mixtures behaved Newtonian until the particle fraction reached 0.15. At this fraction, the mixture started deviate from Newtonian flow; though some average values could still be collected with very high uncertainty. Liquid‐2CaO.SiO2 mixtures and liquid‐MgO mixtures were studied at steelmaking temperature with carefully prepared particle fractions and well controlled conditions. Liquid‐2CaO.SiO2 mixture behaved Newtonian even when the particle fraction reached 0.1. The results of both room temperature measurements and steelmaking temperature measurements were used to examine the applicability of the existing models. Einstein‐Roscoe equation was found to be the only model applicably for the systems studied. No modification of the model parameter was found necessary, though the particles were not spherical.

Synthesis and Characterization of Fe2MoO4 as a Precursor Material for Mo Alloying in Steel

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.

Modelling of slag foaming

In this work, silicone oils of different viscosities were used to simulate slag foaming. The experimental results showed that the variations of foaming height with superficial gas velocity and liquid viscosity do not show simple increasing trends. At a constant viscosity, foaming height increased first and then started decreasing with increasing superficial velocity. Similarly, a maximum foaming height was observed at an optimum viscosity when a constant gas flowrate was applied. The foaming height started decreasing with further increasing viscosity. Based on the experimental data, a semiempirical equation of foaming height was developed. The predictions of the model agreed well with experimental data. The model could also reasonably well explain the industrial pilot trial experiments. The experimental results with paraffin particle additions indicated that a small amount of particle addition moved the onset of foaming to lower superficial velocity. However, the increase in viscosity due to the presence of solid particles was found not the main reason for the increase in foaming height.

Modelado físico de la incidencia de un chorro de aire sobre una superficie de agua

The use of gas jets (oxygen) plays a key role in several steelmaking processes as in the Basic Oxygen Furnace (BOF) or in the Electric Arc Furnace (EAF). Those jets improve heat, mass and momentum transfer in the liquid metal, mixing of chemical species enhancing and govern the formation of foaming slag. In this work experimental measurements were performed to determine the dimensions of the cavity formed at the liquid free surface caused by a gas jet impinging on it; also velocities vectors were measured in the zone affected by the gas jet. Cavities were measured from images from high speed camera and the vector maps were obtained with a Particle Image Velocimetry (PIV) technique. Both velocities and cavities were determined as a function of the main process variables: gas flow rate, distance of the nozzle from the free surface and lance angle. Cavity dimensions were statistically processed treated as a function of the process variables and also as a function of the proper dimensionless numbers that govern these phenomena. It was found thatWeber and Froude numbers govern the cavity geometry. Liquid flow driven by the jet is mainly affected by the air flow rate, lance height and angle.

Foaming in Electric Arc Furnace Part I: Laboratory Studies of Enthalpy Changes of Carbonate Additions to Slag Melts

In the present work, a modified thermal analysis technique was used for studying the heat effect of slag foaming with carbonates addition. Experiments were conducted by sinking limestone and dolomite pieces of defined shapes (together with iron sinkers) in molten slag and monitoring the temperature changes accompanying the decomposition of carbonates. The heat effects of dolomite and limestone decompositions were determined at 1623 K (1350 °C) and 1673 K (1400 °C). It was found that the decomposition energy for dolomite and limestone for the studied slag composition is in the range of 56 to 79 pct of theoretical values, which is linked to the energy-saving effect of slag foaming. No influence of sample shape on decomposition energy was found for both limestone and dolomite.

Thermodynamic studies of MgO saturated EAF slag

Foamy slags are widely practiced in electric arc furnace (EAF) steel production, reducing energy consumption, improving yield, reducing furnace noise, and increasing refractory service life. Control of slag chemistry within a specific range is necessary to achieve maximum benefits from slag foaming. The 'optimum' slag during EAF steel production is MgO saturated, containing a suspension of magnesium wüstite (MgO.FeO) particles. A thermodynamic program, FACTSAGE, was utilised to study a simplified steel slag system containing four slag oxides (MgO–CaO–FeO–SiO2), to predict the dual saturation level of CaO and MgO phases and to predict the MgO slag saturation level with variations in oxygen partial pressure, temperature and slag basicity. Results from thermodynamic calculations indicate that there are linear relationships among slag oxides and slag basicity which can be used to predict and control slag chemistry for foaming. Model data were compared with experimental data and models developed by other researchers.

Improving EAF performance by chemical energy optimisation at Ezz flat steel

An important development of the modular chemical energy system layout, jet flowrate and jet length was implemented in electric arc furnace (EAF) at Ezz Flat Steel plant to reduce electrical energy consumption, avoid skull formation, reduce refractory consumption and improve foaming slag. This development was conducted in stages. The first stage included the implementation of new oxygen jets and a change to the jet distribution in upper shell perimeter water cooled panels. The second stage was to increase the length of the jets and increase the oxygen flowrate. The third stage, increased the jet length and the jet flowrate while the fourth stage, was the application period. The modifications led to a reduction in electrical power consumption of 64 kWh, reduction in refractory consumption of 48% and an increase in furnace productivity of 30%.

Recent Development in Slag Treatment and Dust Recycling

Slags from metallurgical processes are widely used in different fields of application, e.g. in the building industry and as fertilisers. Nevertheless, also these by-products have to be improved to ensure their sustainable use. The treatment of liquid slags, e.g. by changing their composition outside of the steel production process, will lead to interesting new properties of the newly formed products and thus guarantee their use in the future. Moreover, dust and sludges from off-gas cleaning of metallurgical processes are becoming promising resource for coating and alloying elements. The very important element Zn for surface coating is enriched in the dusts, due to the recycling of Zn coated scrap. On the other hand, Zn might run short in the future, so that recovering of Zn from dusts and sludges may become necessary. To improve the efficiency of Zn recovery a dust re-cycling process has been developed for EAF steelmaking by FEhS-Institute. Some interesting side effects are supported by the dust recycling. It has been proved that the slag foaming can be enhanced by dust recycling, even for stainless steelmaking processes. Finally it can be shown that recovery of valuable elements from residues of iron and steelmaking is becoming more and more important. New developed processes are ready to be implemented into the daily steelmaking practise.

Characteristics of supersonic jets in LD steelmaking

In the Linz–Donawitz (LD) steelmaking process supersonic oxygen jets expand into the surroundings formed by hot and dense slag foam thus it is necessary to understand the innate characteristics of supersonic jets when expanding into such surroundings. In this study, the individual influences of both the elevated temperature and high density of the surrounding medium on the jet characteristics are presented. It was found that the supersonic jet characteristics were not affected significantly by the expansion into hot environments with no correlation between the Mach number profiles and changes in surrounding temperature. However, the influence of the dense surroundings on the jet characteristics was profound. The jet velocity was reduced when expanding into a dense medium in comparison with that expanding into a gaseous medium. The peak value of momentum at any cross-section of the jet was not at the axis but in the gas/dense medium interface. The confluence of these factors, i.e. severe reduction in jet velocity and the location of peak momentum within the jet, are expected to change the present understanding of flow dynamics within LD vessels and its influence on refining reactions. Further studies in this area are recommended for better understanding of these phenomena.

Energy Saving Effect of Slag Foaming by Carbonate Additions in EAF Process

Slag foaming has been studied systematically for more than 50 years. The main reason for such interest is a big number of benefits of slag foaming technology in steelmaking, especially for the process in an electric arc furnaces (EAF). There are 2 types of reactions which can be used for slag foaming. The most famous one is the carbon oxidation by oxygen dissolved in metal. Another type of slag foaming reactions is a decomposition of carbonates or other substances, which can produce gas at high temperature. However, it can be concluded that the slag foaming with carbonates is not usual in steelmaking practice. The purpose of the present work is to study the energy effect of slag foaming caused by carbonates decomposition.

Performance Assessment of CO2 Treated Fluxed Iron Oxide Pellets in Basic Oxygen Steel Making Process

Lump lime and iron ore are generally used in BOF as flux and cooling material respectively. Owing to high melting point, poor dissolution property, fines generation and hygroscopic nature of lump lime, delay in process and operational complexities are generally encountered. On the other hand, iron ore charging creates slag foaming. In order to alleviate the above problems and to utilize waste materials, fluxed iron oxide pellets containing waste iron oxides (~70%) and lime fines (~30%) were prepared and subsequently strengthened with CO2 gas treatment. This carbonated fluxed pellets exhibited very good CCS (30 kg/pellet) and DSN (150), suitable for cold handling. The performance of this pellet has been assessed in a laboratory scale bottom blowing converter for its specific use in BOF. The refining characteristic of a liquid bath, prepared with pig iron chips was studied using a laboratory scale bottom blowing converter with three flux conditions namely fluxed pellet plus additional lime, iron ore lump plus lump lime and only lump lime. It has been observed that use of these pellets improves decarburization and dephosphorization, increases the metallic yield, decreases oxygen consumption and reduces foaming. Overall, the developed pellet shows very good application potential in basic oxygen steel making.

Foaming and the Rate of the Carbon-Iron Oxide Reaction in Slag

Foaming in the electric arc furnace is achieved by injecting carbon into slag, where the resulting reaction of the carbon with FeO dissolved in the slag generates gas (CO) that causes the slag to foam. In this research, the rate of the reaction of FeO in slag with carbon and the resulting foam height were measured. In these experiments, the FeO content of the slag ranged from 15 to 45 mass pct, and several different types of carbon were used including graphite, coals, and chars. The rate of the slag-carbon reaction and the consequent CO generation increased with FeO content of the slag from 15 to 45 mass pct. However, the slag foam height reached a maximum at about 25 mass pct FeO and decreased at higher FeO contents. The decrease in foaming is apparently due to a decrease in the foam index or foamability caused by a decrease in viscosity and an increase in density of the slag with FeO content. The results of this work indicate that the foam height is influenced more significantly by the decrease in the foam index compared to the increase in the CO gas generation rate at higher FeO contents. The decrease in the foam index with FeO agrees with that predicted from the slag properties.

Research on Sustainable Steelmaking

The international steel community is faced with the challenge of developing processes that will make steel production more sustainable in the future. Specifically, processes that produce less CO2 and less net waste materials and emissions and that consume less energy are required. This article outlines where energy consumption and CO2 emissions are high and can be reduced. Reductions can be achieved by incremental improvements to existing processes or by a “break-through innovative process”; both strategies are examined. Since most of the energy consumption and CO2 generation occur in ironmaking, research in this area is emphasized. Research on controlling the cohesive zone in the blast furnace, improving the final stages of reduction in direct reduction processes, the use of biomass, and other innovative processes for ironmaking are reviewed. In oxygen steelmaking, improved postcombustion (PC) to allow for more scrap melting is examined. Postcombustion and slag foaming in the electric arc furnace (EAF) in order to reduce energy is reviewed.

Model-based slopping warning in the LD steel converter process

The most prevalent steel-making process is the basic oxygen steel-making (BOS) process. Problems arise when the layer of foaming slag created on the surface of the molten metal exceeds the height of the vessel and overflows, causing metal loss, process disruption and environmental pollution. This phenomenon is commonly referred to as slopping. A method for automatic slopping detection is described in this contribution. The sound signal from a microphone located in the off-gas funnel is processed to obtain an estimate of the slag level in the converter. A model describing the relationship between off-gas flow rate, pressure and the slag level estimate is updated recursively in time. The output error is fed to a change detector yielding a warning system with three alarm levels indicating the persistence of slopping symptoms. The algorithm was tested on data from 100 heats at SSAB Oxelösund. Slopping was correctly detected in 80% of the blows.

Slag Foaming in an Electric Arc Furnace

Slag foaming in an electric arc furnace (EAF) is examined using a mathematical model of the EAF to compute the CO generation rate and slag chemistry and laboratory measurements of the foam index. The foam height limited by either the foam stability or from the amount of slag present was computed for a high productivity furnace using relatively large amounts of pig iron, carbon and oxygen. It was found that for this case the foam is usually simply limited by the amount of slag in the furnace. The effects of the amounts of pig iron, carbon, oxygen and slag were determined. As the amount of carbon as pig iron, coke and coal and oxygen are reduced, the foam height is limited by the CO generation rate and is reduced. The foam decreases towards the end of the process due to lower CO generation rates.