Natural gas conversion to liquid transportation fuels (GTL) through Fischer-Tropsch synthesis (FTS) is an alternative approach compared to the conventional crude oil refining. In a GTL plant, natural gas is first converted to synthesis gas (syngas) and then to liquid fuels in an FT reactor. The distribution of liquid fuels being produced in the FT reactor depends on several factors including catalyst, reactor type, operating pressure and temperature, chain growth probability (α), etc. The change of α along the FT fixed bed reactor is affected by the temperature and H2/CO ratio. In this paper, a typical multi-tubular FT reactor was simulated with a variable α along the tubes length. To do so, the reactor was discretized to 1000 small segments and the α model was modified to fit the wax concentration in the reference FT reactor data with the wax production capacity of 6900 kg/hr. The developed FT reactor model was then used for the plantwide simulation of a GTL flowsheet with larger wax production capacity of ca. 16719 kg/hr. The distribution of chemical species based on variable and constant α were compared. With similar feed syngas composition, the wax mass fraction is 45.34% in the variable α scenario, and is 41.02, 55.7 and 73.57 % when α is fixed at 0.9, 0.92 and 0.95, respectively. In addition, sectioning of the FT reactor into 2 stages was considered to investigate the potential of volume reduction to produce ca. 16719 kg/hr of wax. The results suggest that the staged reactor has nearly 12% lower volume compared to the base-case.

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