Combustion characteristics in an iron ore sintering bed—evaluation of fuel substitution

In an iron ore sintering bed, combustion of solid fuel supplies heat needed for sintering of fine particles and determines the quality of the sintered ores and the productivity of the process. Coke has been widely used as an ideal fuel for this process, but recent attempts to partially replace coke with a less expensive fuel have been considered effective in the real applications. This paper reports simulation results of mathematical modeling of bed combustion as well as experimental observation from scale-downed pot tests. Combustion characteristics of the solid fuel bed are also described and fuel substitution from coke to anthracite coal is evaluated. A numerical model of the 1-D unsteady level considers the processes in the bed of particles: drying, devolatilization, char reactions, gaseous reactions, heat transfer, and geometrical changes of the bed material. The model can treat the solid material as multiple solid phases whose contents include fine particles of iron ore, limestone, coke, and coal. Quantitative parameters are newly defined for characterization of the bed combustion. These include flame front speed, sintering time, duration time in the combustion zone, combustion zone thickness, melting zone thickness, and maximum temperature. Relationships between these parameters and the mechanism of combustion propagation are also investigated. The results show quantitatively that temperature profiles, combustion propagation, and thickness of the combustion zone in the bed are dominated by combustion-related operating parameters. This description is applied to case studies for various coke contents, air supply rates, and fuel characteristics. It is shown that the different reactivity of anthracite in comparison with coke can significantly affect the bed combustion in terms of combustion propagation and the quality of the sintered ores in the upper part of the bed.