Modelling of a bubble column slurry reactor for Fischer-Tropsch synthesis

This work deals with the simulation of a commercial size slurry bubble column reactor for catalytic conversion of syngas (CO+H-2) to liquid hydrocarbons (Fischer-Tropsch synthesis). The reactor was assumed to operate in the heterogeneous or churn-turbulent flow regime and the complex hydrodynamics of the slurry bubble column was described by means of a model, based on an extended experimental program, which takes into account the effect of column diameter, slurry concentration, system properties and pressure on the gas holdup. The reactor model was developed adopting two different classes of bubbles: large bubbles (20-70 mm) which rise through the column virtually in plug-flow, and small bubbles (1-10 mm) which are entrained in the slurry phase (liquid+solid catalyst particles). The slurry phase, together with the entrained small bubbles, was considered completely mixed due to the upward motion of the fast-rising large bubbles. The reaction kinetics was chosen from the literature and referred to a cobalt based catalyst. Design calculations have been carried out for a plant with a 5000 t/day capacity for producing middle distillates. Operating conditions with respect to superficial gas velocity and slurry concentration are suggested so as to achieve the optimum reactor performance. (C) 1999 Elsevier Science B.V. All rights reserved.