  A numerical model is presented, designed to simulate the kinetic and thermal
behaviour of a porous pellet in which any gas-solid reaction is taking place.
Its novelty consists in the fact that it can deal with reactions whether they
are exothermic or endothermic, whether they are equimolar or not, whether they
are reversible or irreversible, and further reactions in the transient regime
and even the possible presence of inert gases and solids can be treated. The
numerical scheme is based on the finite volume method in an implicit
formulation, with a specific treatment of the thermal source term for strongly
exothermic reactions. The model was validated by comparison with analytical and
numerical solutions from the literature and was used to simulate the exothermic
reaction involved in the oxidation of zinc sulphide.
