Modelling and analysis of the combustion behaviour of granulated fuel particles in iron ore sintering

Abstract

The combustion behaviour of solid fuels – for example, coke and biomass char – is an important consideration in iron ore sintering as it determines heat availability for the melt formation process. This behaviour is influenced by the presence of an adhering layer of fine material around the fuel particles. In this study, analytical results for the combustion of single granulated fuel particles – applicable to all Thiele modulus (ϕh) values – are presented. For the conversion of an isothermal carbon particle, the conversion parameter α is found to depend on ϕh and the effectiveness factor ηh. For ϕh < 9, α can be approximated by 0.4ηh, while for ϕh > 9, α approaches ηh/3. The relationship between α and ηh is not altered by the presence of an adhering layer. However, at high temperatures and for reactive fuels, an adhering layer influences the combustion rate significantly. The fuel combustion process in iron ore sintering can be viewed as occurring in three regimes depending on factors such as fuel size, reactivity and temperature. To investigate the effect of fuel properties on sintering performance, the developed combustion model is integrated into a 2D iron ore sintering model. Good comparisons are obtained between model results and experimental data from laboratory sintering tests. In the study of fuel types, model results indicate that when biomass char replaced coke there was significant lowering of flame front temperature and combustion efficiency, while the speed of the flame front down the bed accelerated. These changes can be explained by the higher reactivity of the biomass char and its physical properties which influence the granulation process – resulting in changes in the thickness of the adhering layer and combustion behaviour. The flow-on effect of this on sintering performance is consistent with reported experimental results by other researchers.