(218a) Assessment of an Eulerian-Eulerian Multiphase CFD Framework for a Three Dimensional Modeling of a Trickle Bed Reactor in Counter-Current Operation

Commercial HDT processes usually operate in a trickle-bed regime, with co-current downward flow of gas and liquid over a randomly fixed bed of catalyst particles where reactions take place. It is well known that sulfur removal is strongly inhibited by the competitive adsorption effect of H2S at the sulfided active sites of the catalyst. As a consequence, it is important in these process to maintain the concentration of H2S as low as possible during the reaction to achieve a low sulfur content product at the reactor outlet. According to Ancheyta et al. (2007), a more convenient profile of H2S concentration can be provided by operating the reactor in counter-current mode, for instance, introducing the feed at the top and H2 at the bottom of the reactor. Thus, in the lower section of the reactor, the H2S concentration is lower and H2 is greater, promoting higher reaction rates. The main problems on the counter-current operation are a lower efficiency on the gas-liquid contact; a difficulty in preventing flooding conditions and a higher pressure drop. In order to investigate the above processes in more detail, a three-dimensional fluid-dynamic study of a counter-current trickle bed reactor was carried out using CFD (Computational Fluid Dynamics) techniques with emphasis on determining the pressure drop and the distribution of liquid hold-up in the bed. A CFD tridimensional model based on an Eulerian – Eulerian multiphase approach was used to model the hydrodynamics of the pseudo two-phase flow in a trickle bed reactor (TBR) in counter-current operation. The closure terms for the phase interactions have been based on the fluid-fluid interfacial force balance concept (Attou et al. 1999), which was used and validated to simulate co-current HDT reactors by Gunjal e Ranade (2007). Radial variation of porosity was estimated using the Klerk (2003) distribution. The above set of model equations were implemented inside the commercial software ANSYS-CFX Release 13. The model provided information about phase distribution, velocity profiles, pressure drop liquid hold up for a isothermal trickle bed reactor at laboratory scale in counter-current operation.