(684c) Dynamic Simulation of Metal Oxide Reduction Processes Using a Coupled Reactor-Particle-Continuity Model

Catalysts used in industry often contain cobalt, nickel or copper where the final step in the manufacturing process involves the reduction of the metal oxides with hydrogen. This process is highly complex due to the interplay among the reactor-scale transport, the particle-scale transport and the particle-scale reaction. The limited understanding of these processes hampers the optimal design of reactors. In this paper, a multi-scale reactor model is developed to obtain quantitative description of the reduction process in fixed bed reactors. It should be emphasized that contrary to intensively studied catalytic reactions, solid products are produced in our case.

The concentration and temperature profiles in the fluid phase are described by a 2D transient phenomenological model. The solid phase is described by a spherical particle model in terms of species and energy transport as well as chemical reaction. The intra-particle transport takes bulk and Knudsen diffusion and viscous flow into consideration. The fluid-solid coupling incorporates external mass transfer resistances. Two features are embedded: 1) due to the temporally and spatially varying fluid density, the continuity equation is solved to obtain the velocity distribution; 2) all fluid and solid properties are computed in dependence of local composition, velocity, temperature and pressure.

In this paper, nickel oxide reduction process is studied under industrially relevant conditions. The integral reactor model is first validated by comparing with experiments. Following that, a parametric study is performed to assess the influence of particle characteristics, e.g., size, porosity, tortuosity, pore diameter, etc. After that, the effect of process parameters is studied, such as pressure, composition and temperature of the feed. Besides, dynamic operation of the reduction process is of great interest. Not only the temporal varying profiles but also the (local) water vapor removal strategy are investigated to realize better product quality and higher energy and hydrogen efficiency.