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Several structured packing elements for multiphase tubular fixed bed reactors are compared with regard to catalyst hold-up, heat transfer performance and pressure drop. Structured packings with catalyst coating typically exhibit low pressure drop compared to the conventional randomly dumped packed bed, as well as excellent heat transfer characteristics, but also have considerably less catalyst inventory per reactor volume. A particle-packed structured alternative (packed cross flow structure) exploits the advantages of structured flow, while not sacrificing much in catalyst hold-up (50 v%) compared to a randomly packed bed (65 v%). This alternative retains favorable pressure drop characteristics, which allows the use of reduced catalyst particle size. A numerical analysis of a 1-dimensional reactor model of a fixed bed Fischer–Tropsch process demonstrates that the packed cross flow structure, despite a lower catalyst hold-up than the randomly packed bed, can have a 25% higher C5+ productivity per tube volume than the RPB. The increased productivity results from an increased catalyst effectiveness combined with better temperature control, necessary to keep the catalyst sufficiently selective. |
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