Analysis of rate of hydrogen reduction of porous wustite pellets basing on zone-reaction models.

Abstract

Porous wustite pellets were reduced with hydrogen at 900°C, and reduction curves, position of reaction zone and local fractional-reduction profiles were measured.Basic equations for the grain model were re-examined and solved as they were (unsteady numerical solution), and under quasi-steady (quasi-steady numerical one) and moreover linearization approximations (quasi-steady analytical one). When rate parameter values are selected suitably in each case, measured reduction curves and reaction zone behavior are comparatively well reproduced by the calculated results. Thiele's modulus is about 10-14 under the present experimental conditions and reaction fashion differs much from the one for unreacted-core shrinking model.When the unsteady numerical solution is calculated, reducible oxygen density is divided by M to reduce the computation time; the error at M≤2000 is within a permissible range, although the solution most faithful to the basic equations is obtained at M=1. Comparison between the unsteady and the quasi-steady numerical solutions shows that the latter is an approximate solution having rather good accuracy. The quasi-steady analytical solution is better than the others from practical viewpoint, because its computation time is the shortest and degree of agreement between the measured and the calculated results is much the same among the three.