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Simulation of a natural gas to liquids process with a multi-tubular Fischer-Tropsch reactor and variable chain growth factor for products distribution

Mostafa Zarandi1, Mehdi Panahi1,*, Ahmad Rafiee1,2

1Chemical Engineering Department, Faculty of Engineering, Ferdowsi University of Mashhad, Mashhad, Iran

2Department of Theoretical Foundations of Electrical Engineering, Faculty of Energy, South Ural State University, 76, Lenin Ave., Chelyabinsk, 454080, Russia

 

Abstract

Natural gas conversion to liquid transportation fuels (GTL) through Fischer-Tropsch synthesis (FTS) is an alternative 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 reactor is affected by the temperature and H2/CO ratio. In this paper, the Shell middle distillate (SMDS) FT reactor of Bintulu plant in Malaysia, was used to implement variable α along the fixed bed reactor. The simulated FT reactor was discretized to 1000 small segments and the simulation results including syngas conversion rate and products distribution were compared with the available data of the Bintulu plant. CO conversion is about 95% in the FT reactor and long-chain wax constitutes 45% of the FT products stream. The simulations results are in good agreement with the reported data of the Bintulu plant. The developed FT reactor model was then applied on one train of the Pearl GTL Plant in Qatar (with wax production capacity of ca. 16719 kg/hr) where the same FT reactor technology as the Bintulu plant is used. 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 variable α model, 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 Pearl 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.

Keywords: Gas-to-liquids, Fischer-Tropsch synthesis, syngas, chain growth probability, Pearl GTL plant, staging.

*Corresponding author: Assistant Professor, Dr. Mehdi Panahi, mehdi.panahi@um.ac.ir, Tel.: 0098(51)38805173

 

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