Numerical simulation and parameters optimisation of direct reduction process of iron ore–carbon composite pellet

Abstract

A mathematical model considering heat transfer, mass transfer, porosity change, stepwise reductions of iron oxides and carbon gasification has been developed to investigate the direct reduction process of iron ore–carbon composite pellet. The governing equations were discretised in fully implicit form based on control volume method and numerically solved using tri-diagonal matrix algorithm. The model has been validated by comparison with experimental data from the literature. The effects of some operational parameters have been investigated, and the optimal combination of these parameters is determined by orthogonal test. The results show that the reduction rate increases with the decrease of pellet diameter initially. However, the final degree of reduction increases with the increase of pellet diameter ranging from 5 to 15 mm. Chemical reaction rates increase significantly with the increase of furnace temperature. The degree of reduction for pellet with C/O ratio of 0·8 is lower than pellets with C/O ratio of 1·0 and 1·2 after reduction for 900 s. The degree of reduction is 95·84%, which is high enough in engineering, when furnace temperature, reduction time, C/O mole ratio, and pellet diameter are 1473 K, 10 min, 1·2, and 20 mm, respectively.