Theoretical and Practical Aspects of Dissolution of Lime in Laboratory Experiments and in BOF

Abstract

Plant data on dissolution of lime in combined blown 325 ton converter slag containing low MgO(approx 2-3 mass %), and the top blown 150 ton BOF (approximately 10 % MgO in slag at tap) are analyzed. Kinetics of dissolution of lime has also been investigated in laboratory induction furnace by using a slag composition similar to that in BOF, but with no MgO in slag. Physico-chemical factors affecting the lime dissolution are discussed with particular reference to the effects of size of lime, reactivity of lime and also the role of dicalcium silicate. A kinetic model is developed and tested on plant data. The mass transfer coefficient of lime is found to be strongly dependent on the viscosity of slag-gas-solid continuum. The physical condition of slag can dominate lime dissolution. The kinetic model would greatly help in the estimating the dissolution rate of lime under actual operating conditions. The value of mass transfer coefficient is compared with the reported values in literature. Slag deposited on the top lance in the early part of the blow in a 150 ton BOF shows interesting aspects of lime dissolution.