Slag foaming in bath smelting

Acoustic Analysis of Slag Foaming in the BOF

The control of slag foam that is produced during the Basic Oxygen Furnace (BOF) process has been the subject of significant research. The behaviour of slag foams is complex. Hence, the control of slag foam in the dynamic process of the BOF is challenging. Acoustic analysis of the BOF is one of the most promising methods for the indirect measurement of slag foam height. This paper reviews different studies on the fundamental behaviour of acoustics in liquid foams and various acoustic studies related to determining the slag foam height during the BOF process. Studies on the BOF have been carried out using both cold water models and plant trials, where acoustic measurements taken directly from the process were analysed. These studies showed that the attenuation of sound through liquid foam was influenced mainly by factors such as viscosity, bubble size, and foam height. Current systems are said to be 70 to 87 per cent accurate in detecting and/or predicting slopping events in the BOF, though there is a lack of systematic data in the literature to fully quantify this accuracy. There have been various attempts to combine sound with vibration and image signals to improve the prediction of slopping events in BOFs. The review substantiates the lack of accuracy of the current systems in determining the slag foam height using acoustic analysis and the need to address fundamental questions about the behaviour of sound in dynamic foam, its reliance on different factors, and the relatability of comparing cold model data to industrial data.

Effect of Slag Compositions on Change Behavior of Nitrogen in Molten Steel

The problem of nitrogen pickup in the smelting process of the electric arc furnace (EAF) has not been solved well. Using seven slag–steel equilibrium experiments and theoretical analysis, the relation of the foaming index and optical basicity with the nitrogen capacity of slag was clarified. Meanwhile, the effect of slag composition on the equilibrium distribution ratio of nitrogen and the mass transfer coefficient of nitrogen pickup was also studied. The results show that, with the increase in slag basicity, the nitrogen pickup amount, nitrogen pickup rate, and nitrogen equilibrium distribution ratio LN increase. Increasing the foaming index of slag and reducing its optical basicity will increase the nitrogen capacity of slag, which is conducive to hindering the nitrogen pickup of molten steel. The relationship between slag optical basicity and nitrogen capacity can be expressed as lgCN = −5.59lgΛ − 12.41. With the increase in the Al2O3 content of slag, the nitrogen pickup amount of molten steel decreases and the nitrogen pickup rate decreases. The test with MgO = 7.5% showed the highest nitrogen pickup rate and the highest nitrogen pickup mass transfer coefficient, which were 0.21 × 10−4%/min and 1.97 × 10−4 cm/s, respectively. The test with Al2O3 = 7.5% in slag showed the lowest nitrogen pickup rate and the lowest nitrogen pickup mass transfer coefficient, which were 0.08 × 10−4%/min and 1.35 × 10−4 cm/s, respectively.

Synergetic valorization of basic oxygen furnace slag and stone coal: Metal recovery and preparation of glass-ceramics

A synergetic valorization method was proposed to convert the basic oxygen furnace (BOF) slag and stone coal into ferroalloy and glass-ceramic in this work. Effects of reduction time, temperature, and the mass ratio of BOF slag to stone coal on the reduction were studied. The reduction mechanism was investigated by in-situ observation and dissolution experiments. The effect of sintering temperature on the properties of glass-ceramics prepared from the final slag was further studied. The in-situ observation results indicate that the reduction reactions occurred mainly in the temperature range of 1673-1793 K. The reduction ratio of oxides and size of metal droplets can be improved by increasing reduction time, temperature, and decreasing stone coal addition. The recovered ferroalloys consisted of Fe, Mn, P, and V, which has the potential of returning to the steelmaking process or extracting vanadium. The modified final slag was suitable material for preparing glass-ceramic. Wollastonite-based glass-ceramic with a maximum bending strength of 95.83 MPa was prepared, which could be applied as abrasion-resistant and building decoration materials. Therefore, the present technological route can convert two kinds of industrial solid waste into two kinds of cleaner products and achieve the target of "zero waste".

Bubble Column CFD Model with Effects of Forced Oscillations on Bubble Dynamics

Bubble size distribution has a significant effect on gas holdup, residence time distribution, and mass transfer in bubble column reactors (BCRs). The occurrence of small gas bubbles has potential advantages such as a limited residence time distribution and perfect gas‐liquid phase contact. Gas‐liquid mass transfer in bubble columns can be significantly enhanced by subjecting the liquid phase to low‐frequency vibrations. However, the effect of vibration frequency on bubble formation and hydrodynamic characteristics in BCRs is still not well understood. Herein, a 3D numerical model of a BCR was developed to study the effect of vibration frequency on bubble dynamics under different operating conditions. The Sauter mean bubble diameter was found to be approximately inversely proportional to the vibration frequency.

The Effect of Titanium Carbonitride on the Viscosity of High-Titanium-Type Blast Furnace Slag

In this paper, the effect of titanium carbonitride (Ti(C,N)) on the viscosity of high-titanium-type blast furnace slags was investigated. The different Ti(C,N) contents were achieved by adjusting the reduction degree of TiO2 to reflect the real characteristics of the high-titanium slag. The results show that the viscosity of the slag increased with the increasing Ti(C,N) content and decreased with the rising temperature. A deviation between the measured and the fitted viscosity appeared as the content of the Ti(C,N) was beyond 4 wt%. Furthermore, the apparent viscous flow activation energy of the slag ranged from 106.13 kJ/mol to 235.46 kJ/mol by varying the Ti(C,N) contents from 0 wt% to 4.97 wt%, which was evidently different from the results of previous studies. The optical microscope and energy dispersive X-ray spectroscopy (EDS) analysis show that numerous bubble cavities were embedded in the slags and the Ti(C,N) particles agglomerated in the solidified samples. This phenomenon further indicates that the high-titanium slag is a polyphase dispersion system, which consists of liquid slag, solid Ti(C,N) particles and bubbles.

A critical review of the growth, drainage and collapse of foams

This review focuses on the current knowledge regarding (i) the mechanisms governing foamability and foam stability, and (ii) models for the foam column kinetics. Although different length scales of foam structure, such as air-water interface and liquid film, have been studied to elucidate the mechanisms that control the foamability and foam stability, many questions remain unanswered. It is due to the collective effects of different mechanisms involved and the complicated structures of foam sub-structures such as foam films, Plateau borders and nodes, and foam networks like soft porous materials. The current knowledge of the effects of solid particles on liquid film stability and foam drainage is also discussed to highlight gaps in our present level of understanding foam systems with solid particles. We also critically review and summarize the models that describe macroscopic foam behaviors, such as equilibrium foam height, foam growth and collapse, within the context of the mechanisms involved.

Process-time Optimization of Vacuum Degassing Using a Genetic Alloy Design Approach

This paper demonstrates the use of a new model consisting of a genetic algorithm in combination with thermodynamic calculations and analytical process models to minimize the processing time during a vacuum degassing treatment of liquid steel. The model sets multiple simultaneous targets for final S, N, O, Si and Al levels and uses the total slag mass, the slag composition, the steel composition and the start temperature as optimization variables. The predicted optimal conditions agree well with industrial practice. For those conditions leading to the shortest process time the target compositions for S, N and O are reached almost simultaneously.