The behavior of manganese in oxygen steelmaking

Manganese serves as an important alloying element in commercial grades of steel and high levels of Mn can improve the mechanical properties of steel. [1] The chemical behavior of Mn in Oxygen Steelmaking is complex because the element is readily oxidised in conditions found in steelmaking but the stability of its oxide is a strong function of temperature and slag chemistry, and the oxide can readily revert back to elemental Mn in steelmaking conditions. In many steel plants, manganese ore has been added to achieve high Mn at the end blow. This approach means that the use of relatively expensive ferromanganese (FeMn) can be reduced in the subsequent secondary steelmaking process. [1] Steel plants can also face the problem of high Mn (>1 wt pct) in the hot metal due to the use of lean iron ores with high MnO in the blast furnace, and this can cause operational issues in the steelmaking process.[2

Dynamic modelling of BOF process : comparison of model performance with the plant data

In a top blowing steel making process (BOF), the refining reactions of C, Si, Mn and P are related to several physicochemical phenomena occurring in different zones (e.g. slag-metal emulsion, jet impact zone, slag-bulk metal zone) inside the converter. In earlier publications, the authors have demonstrated a dynamic model, based on the fundamental approach of multiple zone reaction kinetics to simulate the refining of elements (C, Si, Mn and P) in a top blowing steelmaking process (BOF).[1,2] After successful model validation with the literature data from a 200 ton converter[3], simulations have been carried out to assess the model performance with the plant data. Off-line heat data obtained from a 330 ton converter at Tata Steel, Netherlands was used for the model validation. The BOF shop in Tata Steel operates with a wide range of operating and process conditions such as (i) different scrap mix, (ii) dynamic flux addition strategy, (iii) dynamic change in lance position and (iv) top and bottom flow rate. The model predictions of hot metal impurities were validated with the two sub-lance measurements and the simulated slag compositions were compared with the end blow measurements. The possible effect of the uncertainties associated with the measured (or reported) input variables in industrial conditions on the accuracy of the model calculations has been investigated. Further, the role of dynamic change in lance height and flow rate on the slag formation and the hot metal refining has been studied. The present study identifies the critical input variables required for the accuracy in the prediction of the dynamic model in plant conditions and provides a fundamental understanding to control the dynamic process variables in a BOF operation

Dynamic model of basic oxygen steelmaking process based on multi-zone reaction kinetics : modelling of manganese removal

In the earlier work, a dynamic model for the BOF process based on the multi-zone reaction kinetics has been developed. In the preceding part, the mechanism of manganese transfer in three reactive zones of the converter has been analyzed. This study identifies that temperature at the slag-metal reaction interface plays a major role in the Mn reaction kinetics and thus a mathematical treatment to evaluate temperature at each reaction interface has been successfully employed in the rate calculation. The Mn removal rate obtained from different zones of the converter predicts that the first stage of the blow is dominated by the oxidation of Mn at the jet impact zone, albeit some additional Mn refining has been observed as a result of the oxidation of metal droplets in emulsion phase. The mathematical model predicts that the reversion of Mn from slag to metal primarily takes place at the metal droplet in the emulsion due to an excessive increase in slag-metal interface temperature during the middle stage of blowing. In the final stage of the blow, the competition between simultaneous reactions in jet impact and emulsion zone controls the direction of mass flow of manganese. Further, the model prediction shows that the Mn refining in the emulsion is a strong function of droplet diameter and the residence time. Smaller sized droplets approach equilibrium quickly and thus contribute to a significant Mn conversion between slag and metal compared to the larger sized ones. The overall model prediction for Mn in the hot metal has been found to be in good agreement with two sets of different size top blowing converter data reported in the literature

Modeling of droplet generation in a top blowing steelmaking process

Quantification of metal droplets ejected due to impinging gas jet on the surface of liquid metal is an important parameter for the understanding and for the modeling of the refining kinetics of reactions in slag-metal emulsion zone. In the present work, a numerical study has been carried out to critically examine the applicability of droplet generation rate correlation previously proposed by Subagyo et al. on the basis of dimensionless blowing number (N B). The blowing number was re-evaluated at the impingement point of jet with taking into account the temperature effect of change in density and velocity of the gas jet. The result obtained from the work shows that the modified blowing number N B,T at the furnace temperature of 1873 K (1600 °C) is approximately double in magnitude compared to N B calculated by Subagyo and co-workers. When N B,T has been employed to the Subagyo’s empirical correlation for droplet generation, a wide mismatch is observed between the experimental data obtained from cold model and hot model experiments. The reason for this large deviation has been investigated in the current study, and a theoretical approach to estimate the droplet generation rate has been proposed. The suitability of the proposed model has been tested by numerically calculating the amount of metals in slag. The study shows that the weight of metals in emulsion falls in the range of 0 to 21 wt pct of hot metal weight when droplet generation rate has been calculated at ambient furnace temperature of 1873 K (1600 °C)

Dynamic model of basic oxygen steelmaking process based on multi-zone reaction kinetics : model derivation and validation

A multi-zone kinetic model coupled with a dynamic slag generation model was developed for the simulation of hot metal and slag composition during the BOF operation. The three reaction zones, (i) jet impact zone (ii) slag-bulk metal zone (iii) slag-metal-gas emulsion zone were considered for the calculation of overall refining kinetics. In the rate equations, the transient rate parameters were mathematically described as a function of process variables. A micro and macroscopic rate calculation methodology (micro-kinetics and macro-kinetics) were developed to estimate the total refining contributed by the recirculating metal droplets through the slag-metal emulsion zone. The micro-kinetics involves developing the rate equation for individual droplets in the emulsion. The mathematical models for the size distribution of initial droplets, kinetics of simultaneous refining of elements, the residence time in the emulsion, dynamic interfacial area change were established in the micro-kinetic model. In the macro-kinetics calculation, a droplet generation model was employed and the total amount of refining by emulsion was calculated by summing the refining from the entire population of returning droplets. A dynamic FetO generation model based on oxygen mass balance was developed and coupled with the multi-zone kinetic model. The effect of post combustion on the evolution of slag and metal composition was investigated. The model was applied to a 200-ton top blowing converter and the simulated value of metal and slag was found to be in good agreement with the measured data. The post-combustion ratio was found to be an important factor in controlling FetO content in the slag and the kinetics of Mn and P in a BOF process

Dynamic model of basic oxygen steelmaking process based on multi-zone reaction kinetics : modelling of decarburisation

In a previous study by the authors (Rout et al.[1]) a dynamic model for the BOF, employing the concept of multi-zone kinetics was developed. In the present work, the kinetics of decarburisation reaction is investigated. The jet impact and slag-metal emulsion zones were identified to be primary zones for carbon oxidation. The dynamic parameters in the rate equation of decarburisation such as residence time of metal drops in the emulsion, interfacial area evolution, initial size and the effect of surface active oxides have been included in the kinetic rate equation of the metal droplet. A modified mass transfer coefficient based on the ideal Langmuir adsorption equilibrium has been proposed to take into account the surface blockage effect of SiO2 and P2O5 in slag on the decarburization kinetics of a metal droplet in the emulsion. Further a size distribution function has been included in the rate equation to evaluate the effect of droplet size on reaction kinetics. The mathematical simulation indicates that decarburization of the droplet in the emulsion is a strong function of the initial size and residence time. A modified droplet generation rate proposed previously by the authors has been used to estimate the total decarburization rate by slag-metal emulsion. The model prediction shows that about 76 pct of total carbon is removed by reactions in the emulsion, and the remaining is removed by reactions at the jet impact zone. The predicted bath carbon by the model has been found to be in good agreement with the industrially measured data

The behavior of manganese in oxygen steelmaking

The chemical behavior of manganese in oxygen steelmaking is complex because the element is readily oxidized in conditions found in steelmaking, and the stability of its oxide is a function of temperature and slag chemistry. This results in distinct oxidation and reversion stages during the steelmaking cycle. Recently, a multi-zone model (developed by the authors) of oxygen steelmaking has successfully predicted the plant behavior of manganese but also highlighted how the generation of droplets and their temperature play an important role in the kinetics of the process. This new understanding should result in improved control of this important alloying element