Interaction of Reducing Gases with Pellets: Cellular Automaton Simulation

Ore pellets are commonly used in the blast furnace to produce pig iron and are practically the only raw material suitable for MIDREX and HYL furnaces. Therefore, it is of great importance to improve pellet quality and hence the efficiency of steel production. The reducing properties of the ore pellets are critical to furnace performance. In the present work, the role of pellet cracking in changing the reduction rate is studied. Cellular automata are used in simulating the pore structure of the pellets in a stream of reducing gas. The application of this method is shown to be feasible. The overall picture of the process obtained corresponds to empirical data. Reduction of the pellets’ pore structure by gas occurs in two stages, which differ in the rate of mass transfer. In the first stage, the reduction rate depends exclusively on the contact area of the phases. After surface reduction is complete, the reduction rate is determined by the gas diffusion within the pellet’s mineral component. Pellet cracking markedly increases the reduction rate in the initial stage: the number of reduced grains may be increased by as much as 100%. Positive feedback between the reduction rate and the growth rate of the cavity volume in the pellet is noted: these processes are mutually accelerating. The limiting factors are processes at the surface and gas transfer. In practice, there is no need to produce pellets with very high (>95%) hot strength. Such pellets, while formally meeting the technical requirements, are reduced very slowly and retard the smelting process.