Critical evaluation of role of viscosity and gas flowrate on slag foaming

Slag foaming is a fundamental aspect in both electric arc furnace and oxygen converter steelmaking. In the latter, the unstable foaming can cause the undesired phenomenon of slopping, which implies significant blow-up of the material contained in the converter. The foaming has been studied on the basis of different approaches; theoretical studies usually based on a dimensional physical analysis and experimental studies. In all the cases, strong non-linear relations among the involved factors of influence have been highlighted, but some lack of consistency among the different results has emerged, especially about the role of the surface gas velocities and the viscosities of the slag and foam. Therefore, in this study the discussion about the foaming phenomenon has been evaluated through experimental trials developed using oil at different temperatures in order to take into account the effect of the change of the viscosity. The study has permitted the clarification of the reason of the collapse of the foam at a high gas flowrate; this phenomenon being associated to the increase in the average bubble size provided to the already formed structure of the foam. Via the experimental observations made at different gas flowrates and the development of simple analytical relationships, the viscosity has been confirmed to be an important stabilising factor, because it does not favour the liquid drainage, and low temperatures favour foam stabilisation, increasing its height.