Optimization of electroslag melting towards to titanium morphology improvement in combined Kroll process

Abstract

Purpose The paper aims to optimize calcium difluoride electrical melting process towards creating titanium production with improved morphology by combining titanium reduction and electroslag melting processes. The study aims to explore optimal electrical heating power in the slag supplied via tungsten electrode and formation of a stable skull layer on water-cooled walls of a cylindrical stainless steel reactor, which is crucial for electroslag melting. Design/methodology/approach The multi-physical numerical modelling approach using commercial software COMSOL Multiphysics is presented in the paper by coupling electrical, heat transfer and fluid flow problems. The slag material phase change and corresponding changes of physical properties such as electrical conductivity and viscosity are modelled by step function, sharply changing value of parameter near the phase change temperature. A parametric study of applied electrical power has been carried out to find optimal conditions for the skull-layer formation. Findings The paper provides an estimation of necessary electrical power to avoid overheating or solidification of the top layer of slag, which is unacceptable for the combined Kroll process. The study also revealed important poloidal buoyancy flow with characteristic velocity of few cm/s of in the reactor, which governs the heat transfer process and formation of the skull layer. Research limitations/implications The presented simplification in numerical model offers high calculation speed but lacks fully developed phase change model, e.g. excluding latent heat. Also, heat transfer through radiation is neglected in the model. Originality/value The paper presents an original way to overcome the complexity of modelling slag electrical melting/solidification phenomena using temperature-dependent properties with step functions.