Rafael L. Espinoza

Multiplicity and sensitivity analysis of Fischer–Tropsch bubble column slurry reactors: plug-flow gas and well-mixed slurry model

Existence of multiple steady states of Fischer–Tropsch (FT) synthesis has been reported experimentally as well as theoretically even in simple stirred tank slurry reactors. Bhattacharjee, Tierney, and Shah (1986) have found steady-state multiplicity in product distribution and heat generation rate in their experiments on supported ruthenium catalyst. Shah, Dassori, and Tierney (1990) have subsequently provided an explanation of this observation based on the analysis of heat generation and dissipation curves. They maintained that ignition should be avoided since, once it occurs, the normal FT synthesis reaction would be switched to the methane-forming mode seemingly never to return. This is because the catalyst could su=er serious deactivation on exposure to the high temperature resulting from the ignition. Recently, Song, Ramkrishna, Trinh, andWright (2003) have reported more complex experimental observations for an FT stirred tank slurry reactor with cobalt catalyst. The operating state of the FT process suddenly jumps from the normal wax-producing mode to the undesirable methane-forming mode accompanying the abrupt temperature lift. This multiplicity behavior is peculiar in the following two senses: (i) this happens sporadically, not always, and (ii) the normal wax-producing mode was, contrary to the interpretation by Shah et al. (1990), eventually recovered after a couple of hours. A plausible scenario explaining this peculiar multiplicity behavior was proposed by Song et al. (2003) using rigorous nonlinear analysis. It was found that decrease of the Stanton number for heat transfer (StH ) could be responsible for the @rst jump, while a decrease of the DamkA ohler