Abstract:
Trickle-Bed Reactors (TBRs) are widely utilized in industrial applications. One of
the main industrial applications of TBRs is transforming a gaseous mixture of hydrogen
and carbon monoxide, called syngas, to environment-friendly synthetic liquid fuels, via
Fischer-Tropsch Synthesis (FTS), which is a strongly exothermic reaction.
The aim of this work is to develop a pseudo-homogeneous two-dimensional (2D)
Fischer-Tropcsh Packed Bed Reactor (FTPBR) model in order to investigate the use of
slender packed bed reactors for FTS. This will facilitate the excess heat removal from the
bed as well as enhance the performance. To accomplish this objective; two main studies
have been conducted, which are (i) hydrodynamic study and (ii) then using its results to
develop a FTPBR model. The modeling was carried out using the Finite Element Analysis
(FEA) software known as COMSOL Multiphysics 5.6.
Firstly, it was confirmed that the Eisfeld and Schnitzlein drag force model should
be applied in the momentum balance equation of a two-dimensional pseudo-homogeneous
model for low aspect-ratio packed beds. Moreover, a novel 2D modeling approach was
proposed for packed bed reactors with an aspect ratio of 2, under laminar flow conditions,
mainly of particle Reynolds number lesser than 111.
Secondly, based on the Eulerian mixture approach, a mathematical 2D pseudo
homogeneous model of the FTPBR was developed and validated by confronting its
simulated results against those of models of literature as well as by conducting a consistent
error discretization uncertainty study. Then it was exploited for the optimization of large
scale FT reactor as well as to optimize and design a small-scale FT reactor. For each scale,
two cases were investigated. While the feedstock of the large-scale cases was natural gas,
the small-scale cases used biomass as feedstock. For each case, four PBRs with different
aspect ratios ranges from 2 to 15.33 were simulated.
It has been found that, the large PBR is the optimized reactor for the large scale,
which can be used in a GTL plant to process 170000 m3 of natural gas - at standard
conditions - for producing more than 626 tons of C5+ per day. Otherwise, the slender PBR
with aspect ratio of 4 is the most efficient for the small scale. This reactor is 2 m long and
1916 mm in diameter, which is composed of 6698 tubes arranged in triangular pattern.
Besides, it was designed to be fitted into a mobile micro-refinery to process 6 tons of wood
chips or 6.6 tons of municipal solid waste per day, to daily produce 4827.16 kg/d and
281.55 kg/d of C5+ and LPG, respectively.
