Abstract

This is the last in a series of papers on the numerical dynamic simulation of a single, spherically symmetric, porous pellet in which diffusive transport and chemical reactions are taking place. It describes the extension of the technique to multiple fluid and solid reactants and products, underoing multiple reactions. As shown previously, the particular form of the model in which explicit references to individual fluid species fluxes have been eliminated offers favorable numerical characteristics. This paper describes the considerable additional effort, by comparison to the binary fluid system of the previous paper, required to accomplish the flux elimination. The fluxes can be replaced by functions of the fluid species mole fractions and the total molar flux if the transport equations can be inverted. An algorithm for obtaining a unique solution to the Stefan—Maxwell equations is described in detail with references to other approaches in the literature. This permits formulation of the model as an index one set of differential/algebraic equations suitable for numerical solution by a general-purpose DAE solver. We briefly describe a code, MSRS (Multispecies Shale Retorting Simulator), which uses the DAE solver DASSL to simulate nonisothermal reacting/diffusing pellet dynamics. Two example problems are presented: a smaller, three fluid/two solid/one reaction simplified model of oil shale combustion, and a larger, nine fluid/10 solid/15 reaction simulation of in situ oil shale retorting with time-dependent boundary conditions. Both models were run with coarse and fine spatial solution meshes. Simulator performance is discussed and several modifications to the models made to speed up execution.

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