Development of a numerical sizing tool for a solid-gas thermochemical transformer .1. Impact of the microscopic process on the dynamic behaviour of a solid-gas reactor

The two major categories of models developed for sizing a solid-gas thermochemical transformer have different objectives. The local models, based on the local conservation equations allow the optimisation of one of the process components. The global models allow the description of the complete process, and more particularly show the complex couplings between the different components of a single unit. The identification of the kinetic parameters for three forms of kinetic law, from recent experimental results obtained by differential microcalorimetry under pressure, allows the quantification of the confidence interval related to these three laws, firstly microscopically (a few milligrams of reactant). The effect of these three laws on the dynamic simulation of a reactor containing a few kilograms of product is then compared with the experimental results obtained on a thermochemical transformer prototype. Moreover, the representation of the non-equilibrium conditions (P-c, T-c) by a single control parameter (theta) proportional to the affinity of reaction leads to the definition of an equivalent temperature for the reactive medium and allows a much easier global model to be obtained for sizing a reactor. On the one hand, the comparison model/experiments shows the limits for using the microscopic kinetic laws in a global model, and on the other hand, the reliability of the equivalent temperature model. (C) 1997 Elsevier Science Ltd.