Alkali effect on the Iron making processes

Abstract

Abstract The impurities in raw materials pose many problems to the smooth operation of the iron making processes and have adverse effects on the final product. One amongst such impurities are the alkali elements (Na/K). Alkali elements enter the iron making processes mainly from the charge materials (Iron ore and Coke). The type of iron ore charge materials (lumps/ sinter/ pellets/ briquettes) also influences the alkali intake. The effects of alkali elements, present in iron ore charge and coke are different and have to be tackled accordingly. The adverse impacts of alkali content are decrement in mechanical strength of the charge materials, formation of low melting phase, alkali recirculation, process irregularities and refractory damage. The influence of alkali present in different charge materials has to be studied methodically to understand the adverse effects of alkali elements on the iron making processes. In this thesis, an attempt has been made to study the impact of alkali present in different forms of iron ore charge materials i.e. lump ore, sinters, pellets and briquettes, have on the reducibility of the ore under various alkali concentrations with varying time and temperature. Different iron ore charge materials have been tested under both direct reduction conditions as well as conditions replicating a blast furnace. Optimal alkali load that can be allowed to enter the furnace without causing too much of irregularities, has been found out with the help of statistical modelling via Box Behnken Design Modelling. The effect on the strength of the charge (where possible) has also been investigated to understand the contribution of alkali elements towards generation of fines. Similar type of experiments, have also been carried out for coke to understand the effect of alkali on coke along its catalytic effect on Boudouard reaction. Kinetic study of the reduction of different iron ore charge material under varied alkali loading and reduction conditions has also been done followed by characterization of the reduced samples. The kinetic study of bouduard reaction of coke under different alkali loading has also been carried out. The alkali effect on the activation energy of bouduard reaction has also been carried out. At last, an attempt has been made to find out some remedies to control the irregularities caused by the alkali intake; through alkali removal via smelting.