The effect of gas and solids maldistribution on the performance of moving-bed reactors: The reduction of iron oxide pellets with hydrogen



A mathematical formulation is presented describing the reduction of iron oxide pellets with hydrogen in a counterflow moving-bed arrangement under conditions such that both the gaseous and the solids streams may be maldistributed. This maldistribution is imposed on the system by prescribing a radial variation in the void fraction and the particle size, together with a radial variation in the axial velocity of the solid stream.

In the formulation, allowance has been made for realistic chemical kinetics and nonisothermal behavior. Computer results are presented for both the maldistributed system and for base line cases where uniform gas and solids flow have been postulated.

It was found that maldistribution may play a very marked role in affecting the performance of the system, in particular, when the gas and the solid streams are mismatched, for example, preferential flow of gas near the walls and preferential flow of solids in the central core.