Effects of intraparticle heat and mass transfer during devolatilization of a single coal particle

The objective of the present work is to elucidate the influence of intraparticle mass and heat transfer phenomena on the overall rate and product yields during devolatilization of a single coal particle in an inert atmosphere. To this end a mathematical model has been formulated which covers transient devolatilization kinetics and intraparticle mass and heat transport. Secondary deposition reactions of tarry volatiles also are included. These specific features of the model allow a quantitative assessment to be made of the impact of major process conditions such as the coal particle size, the ambient pressure and the heating rate on the tar, gas and total volatile yield during devolatilization. Model predictions are compared to a limited number of experimental results, both from the present work and from various literature sources

Etude hydrodynamique d'une colonne à bulles 2D en présence d'additifs faiblements concentrés

Un traitement d’images, issues de cinématographie rapide en colonne 2D, donne la distribution de taille de bulles d’air dans l’eau pure ou additivée. La technique, basée sur l’analyse de nombreuses bulles, nécessitant leur identification et leur suivi en cas de rupture ou coalescence, est tout d abord décrite puis utilisée pour préciser l’influence d’ajout de silice et/ou de sulfate de sodium dans de l’eau pure. Le peu d’effet observé sur la rétention gazeuse lors d’addition de silice résulte de la compensation de l’augmentation du diamètre des bulles par la réduction d’aire interfaciale. Au contraire, l’ajout de sel augmente fortement la rétention gazeuse. Enfin la silice assez concentrée annule cet effet inhibiteur de coalescence. L’outil de traitement d’images donne accès à des données statistiques originales de rupture et coalescence

Efficient simulation of periodically forced reactors with radial gradients

The aim of this paper is to present a limited memory iterative method, called the Broyden Rank Reduction method, to simulate periodically forced processes in plug-flow reactors with radial gradients taken into account. The simulation of periodically forced processes in plug-flow reactors leads to the development of partial differential equations that are normally solved in time using dynamical simulation. Depending on the convergence properties of the system at hand, the number of cycles that needs to be computed up to a cyclic steady state is reached can be large. Therefore direct iterative methods are essential in order to capture the long time dynamics of such systems. In order to overcome severe memory constraints many authors have reverted to pseudo-homogeneous 1D models and to coarse grid discretization, which renders such models inadequate or inaccurate. The results that we present show that the long time dynamics actually depends on the radius of the reactor and, hence, the full 2D model is essential in order to simulate periodically forced processes in plug-flow reactors accurately