The Use of Thermodynamic Modeling to Examine Alkali Recirculation in the Iron Blast Furnace

It is widely recognized that alkali metals, such as, potassium and sodium can cause operational problems in the iron blast furnace. These elements can influence properties, such as, the softening and melting of ores, formation of scaffolds, coke properties, and refractory life. It has been established that recirculation of these elements occurs within the furnace. In the lower furnace vaporization occurs in the high temperature hearth and bosch regions, and condensation occurs in the upper furnace below or in the cohesive zone. For these reasons the input of alkalis into the furnace is strictly controlled. Optimized thermodynamic databases describing slags in the system Al2O3-CaO-FeO-Fe2O3-Na2O-K2O-MgO-SiO2 have been developed and, combined with the computer software FactSage; these databases have been used to predict the possible behaviour of alkalis in the blast furnace and to examine the effects of changing process variables on reactor performance. To demonstrate this approach to process modeling the furnace is considered as a two-stage equilibrium reaction system and the results of initial analysis are reported.