Reduction Of FeO In Slag Research Articles

Application of sessile drop technique (SDT) for study of reduction of FeO in slags: reduction by solid carbon as well as solute carbon

With growing importance of smelting reduction processes, experimental research to understand reduction of FeO in molten slag and the foaming behaviour associated therein have assumed greater relevance. In a previous paper, experimental data on reduction of FeO in molten slag in a 30 kW capacity induction furnace have been reported. The present study used around 250 g slag in each experiment was concerned with influence of FeO concentration in molten slag and temperature on foaming and kinetics. The present paper describes a study on the same system carried out using the sessile drop technique (SDT) which, although it uses very small (∼25 mg) sample size, is extremely versatile. Moreover, SDT allows one to actually see the reaction occur. An attempt has been made to correlate kinetic data obtained using the present set-up with the data where much larger sample sizes were used. Both solid carbon and solute carbon have been employed in reduction studies.

Mathematical Modelling and Experimental Investigation of Coke Reduction of FeO in Slag

Mathematic model development and experimental investigations were carried out for the reduction of FeO in slag by coke. Rate expressions for the reduction limited by the different steps and through different reaction routes were proposed. In the experimental investigation, the FeO reduction was found to be a first order and irreversible reaction; the reduction rate increased with increasing temperature and the FeO content in slag, and decreased with increasing ash content in the coke. Low CO2/CO ratio in the product gas and preferential reduction of FeO over SiO2 in slag were observed in the reaction system. The proposed reaction mechanisms were discussed with the observed kinetic phenomena. The reduction of FeO in slag by coke was found most likely to be jointly dominated by the mass transfer of FeO in slag and the chemical reactions at slag‐coke, slag‐gas or slag‐metal interfaces.

Prediction of coal slag foaming under gasification conditions by thermodynamic equilibrium calculations

In slagging gasifiers, slag foaming can cause serious operational problems, so there is a need for investigation into the conditions causing slag foaming. Viscosity experiments were carried out examining viscosity, extent of swelling and Fe formation. Although extensive swelling was not observed, FeO reduction was observed under an N2/CO gas atmosphere, but not under CO2/CO. In order to predict FeO reduction conditions in the gasifier, a model for an adiabatic equilibrium gasifier was developed. The gas composition, the amount of gas to slag, and Po2 were calculated for a slurry-feed gasifier, and the results of the calculation were used to predict the reduction of FeO in slag by using FactSage. Under typical gasification conditions for Denisovsky coal, the predicted P o2 in the gasifier was not low enough to cause FeO reduction. The FactSage simulation for the viscometer conditions predicted no FeO reduction under a CO/CO2 atmosphere, but did predict Fe formation under CO/N2 conditions. At a 20% CO concentration, FeO reduction starts at temperatures above 1,600°C. Since the slag has a low viscosity at 1,600°C, the oxygen bubble may have escaped as it formed. Therefore, slag foaming, caused by FeO reduction in the slag, can only occur when the right conditions of viscosity and oxygen partial pressure are met.

Reaction Rates and Swelling Phenomenon of Fe–C Droplets in FeO bearing Slag

The reduction of FeO in slag by an iron droplet, decarburisation of the droplet and the droplet swelling phenomenon during slag-metal droplet reaction were analyzed by a kinetic model. Diffusions in the slag phase, diffusions throughout the droplet, interfacial reactions, equilibrium relations and homogeneous nucleation of gas bubbles within the droplet were incorporated in the model.During an Fe–C droplet reaction with FeO bearing slag, decarburisation rate increases with increasing FeO in slag, carbon in the droplet and the droplet size, but the rate decreases with increasing silicon in metal and ambient pressure. The decarburisation rate in unit surface area of the droplet increases with increasing the droplet size. Slow decarburisation during the initial stage of the reaction was suggested by the model, and the desiliconisation and oxygen absorption of the droplet were found to be responsible for this initial slow decarburisation. The initial slow decarburisation is pronounced when the droplet contains higher carbon and silicon, or when the reaction occurs under higher pressure and with the slag containing lower FeO. CO bubble generation within the droplet was suggested to cause the swelling of the droplet. The occurrence of swelling is promoted when the droplet contains higher carbon and lower silicon, slag contains higher FeO, or when the droplet is small, and the reaction occurs under lower pressure.

Reduction of FeO in Slag with Coal Char.

Recently, many blast furnaces have increased pulverized coal injection. Unburnt coal char is generated from pulverized coal injection and a portion of it remains in the slag. This interferes with tapping by increasing slag viscosity, and can make blast furnace operation unstable. Reduction of FeO with different types of coal was measured in simulated blast furnace slags at 1450°C, using a constant volume pressure increase (CVPI). The reaction rate of FeO was observed to be independent of the type of coal used regardless of different components such as volatile matter and ash. The measured rates at 1.0% and 3.0% of FeO in the slag were 2.77 × 10 -7 and 1.58 × 10 -8 mol/cm 2 s respectively. The overall rate is controlled by a series of processes such as the reaction of CO 2 with C, CO with FeO in slag, liquid phase mass transfer of FeO in the slag, and gas phase mass transfer. For low FeO contents, when the gas evolution rate is low, liquid phase mass transfer is the primarily controlling mechanism. A model to predict the amount of char in the slag at tap based on these results is presented.

Characterization of Slag-Metal Droplet-Gas Emulsion in Oxygen Steelmaking Converters.

Metal droplets of various sizes are ejected from the jet impact zone in oxygen steel making converters. The residence time of these droplets in the surrounding gas-slag mixture is calculated for different operating conditions in top blown converters. A new dimensionless emulsion number, En, based on the ratio of the residence time of the metal droplets to the residence time of gas bubbles in liquid slag is proposed. This emulsion number is found to be strongly dependent on the ratio of lance height to the throat diameter of De Laval nozzle. The blowing regimes followed in three plants are analyzed in terms of emulsion number. The reduction of FeO in slag by dissolved carbon in metal droplets also depends upon emulsion number and, in turn, decides the lance height chosen at various stages of the blow as well as lime dissolution, slag formation and slopping. The emulsion number can be used as an effective tool to control slag formation behaviour.

Rate of reduction of FeO in slag by Fe-C drops

The rate of reduction of FeO in slags by Fe-C drops plays an important role in several metallurgical processes, including iron bath smelting. In this study, the rate of this reaction was determined by measuring the volume of CO generated as a function of time, and the reaction was observed by X-ray fluoroscopy. The drops entered the slag in a nearly spherical shape, remained as single particles, and for the major portion of the reaction remained suspended in the slag surrounded by a gas halo. The rate was found to decrease with carbon content for alloys with low sulfur contents. The rate decreased significantly with increasing the sulfur content. Based on the results and a comparison of the calculated rates, for the possible rate-controlling mechanisms, a kinetic model was developed. The model is a mixed control model including mass transfer in the slag, mass transfer in the gas halo, and chemical kinetics at the metal interface. At high sulfur contents (>0.01 pct), the rate is primarily controlled by the dissociation of CO2 on the surface of the iron drop. At very low sulfur, the rate is controlled by the two mass-transfer steps and increases as the gas evolution from the particle increases.

Reduction of FeO in Molten Slags by Solid Carbon in the Electric Arc Furnace Operation

the course of operation of 70 l UHP furnace in Chita Plant, Daido Steel, solid carbon has been injected in order to facilitate the reduction of FeO in slag and to improve the energy saving and heating efficiency. In this paper, the effect of the injection method on the reduction rate of FeO in slag is discussed in relation to the quality and size of carbon powder injected, injection rate and nature of molten slag. Moreover the relation between the fundamental data of waste gas and the degree of slag reduction has been comfirmed. The results obtained are summarized as follows:(1) Volatile matter in solid carbon gives a large influence on the reducing reaction. In the coke of higher content of volatile matter, the reduction is controlled by the chemical reaction, while in the coke o f lower content of volatile matter, the reduction is controlled by the transport of FeO in slag.(2) The reduction rate depends on the basicity of molten slag. The reduction rate increases as the basicity of molten slag increases.(3) Estimation of carbon content of molten steel for a rapid operation is found to be possible by the use of the fundamental data of waste gas.

Reduction of Molten Iron Oxide and FeO Bearing Slags by H2-Ar Plasma

(I) Reduction of molten iron oxide and FeO bearing slag by H2-Ar plasma was studied using water cooled Cu crucible. The sample weights were 25 to 75g, the flow rate of mixture-gas was 20l/mm and DC electric power of plasma was 8.3kW. Results obtained were as follows:(1) The reduction of molten iron oxides proceeds linearly with time and the reaction rate is proportional to the partial pressure of atomic hydrogen. Therefore, it is considered that the rate determining step is the chemical reaction between FeO and the atomic hydrogen formed by thermal dissociation in the plasma.(2) The rate of reduction of FeO bearing slag is lower than that of molten iron oxide and is proportional to the FeO concentration in slag. It is presumed that the reduction rate is controlled by both the chemical reaction rate of FeO with atomic hydrogen at the gas-solid interface and the mass transport rate of FeO across the boundary layer between the interface and the molten slag bulk.(3) The reduction of molten iron oxide and FeO bearing slag by H2-Ar plasma takes place only on the cavity formed at the surface of melt by the momentum of plasma jet gas.(II) Continuous melting of pre-reduced ore powder, obtained by a fluidized bed reduction was examined using MgO crucible and H2-Ar plasma.Following results were obtained:(1) Carry-over loss of the pre-reduced ore powder during the melting in plasma arc furnace was small, when the condition of powder feeding and plasma arc were properly chosen.(2) Reduction of FeO in slag, accompanied in fed material, by H2-Ar plasma, could be described by a simple model of continuous melting and reduction, based on experimental results of the reduction of FeO bearing slag as described (1-2).With this model, the rate of reduction during continuous melting was determined.