The melting properties of tuyere slags with and without flux injection into the blast furnace

Abstract

A laboratory study concerning the melting properties of tuyere slags has been conducted. The melting-point measurements of various specimens, consisting of coke ash, coal ash and fluxes (BOF slag, burnt lime and burnt dolomite), corresponding to the tuyere slags formed in front of the tuyeres with or without flux injection, have been performed in a high-temperature microscope. Theoretical estimations of melting points have been made based on the chemical composition of the tuyere slag specimens. The results have shown that injection of fluxes has quite a positive effect on the melting properties of the tuyere slag. The melting point of the tuyere slag decreases and the temperature interval between softening and complete melting of the tuyere slag becomes narrower. Compared to the injection of burnt lime and burnt dolomite, the injection of BOF slag will result in still better tuyere slag properties in terms of lower flow point and narrower temperature interval between softening and melting. The differences in melting behaviour in the tuyere slag specimens indicate that injection of BOF slag will also give the tuyere slag a lower viscosity compared to injection of burnt lime or burnt dolomite at the same levels of slag basicity B2.