Segregation of Carbon Paste in a Smelting Electrode

Abstract

An industrial problem concerning segregation in carbon paste is described. Billets of paste, which are a mixture of coke and pitch, are fed into a steel tube in a furnace, and the tube is lowered at a rate of about 0.75 m day −1 . In the tube, the pitch is defonnable, and the paste is essentially a very viscous two-phase participate medium. The grain size distribution is essentially bimodal, consisting of coarse (˜10 mm) particles in a distribution of finer (100 μm) particles. Segregation occurs near the walls of the tube, leading to a lower content of coarse particles; such segregation is unwanted, and so the length of this segregated region is required to be minimized. It is suggested that segregation is due to the stiffness of the coarse particulate mixture, which is less able to deform than the pitch/fines mixture. Consequently, the length of the segregated region is controlled by the coarse mixture viscosity, and an expression is derived for the segregation length.