(560ja) Validated CFD Simulations of a Bench-Scale Fixed Bed Fischer-Tropsch Reactor

The
Fischer-Tropsch synthesis (FTS), which converts syngas into liquid fuel, has
a very important application and perspective. The fixed
bed reactor (FBR) is one of the most competitive and mature reactors applied in
small scale FTS, such as biomass to liquid fuel process (BTL). Compared
to lab scale FBR, heat transfer is more important and the temperature profile
along the catalyst bed cannot be ignored in a bench scale FBR. In this study, a bench scale reactor with 50 mm diameter
and 1 000 mm length was specially designed for temperature measurement and
employed in FTS. Four thermocouple sheaths were placed at different radial
positions of the reactor. Each thermocouple can slide smoothly inside the sheath
and measure the temperature in axially direction. Serial
experiments were conducted at low temperature FTS conditions (2 MPa and 458K)
with Co-based catalyst. The temperature distributions and reaction performance were investigated when changing the
inert gas (nitrogen) content and gas hourly space velocity (GHSV) respectively.

Computational
fluid dynamics (CFD) simulation is an efficient access for certain chemical
operating unit designing, result prediction and operating condition optimization. A 3D pseudo-homogeneous FBR model including the oil
bath on the shell side was set up and solved by Fluent in this study. Thermal equilibrium was assumed between the gas phase and the
solid phase (catalyst bed). A widely used semi-empirical kinetic model was
implemented to describe the FTS. When separately comparing the
temperature profile (Figure 1) and reaction performance (CO conversion, CH₄
selectivity and C₅₊ hydrocarbon selectivity) from simulation results
to experimental data, it showed a good agreement. Based on
this validated model, numerical experiments can be conducted to give a precise
guideline for further studies on optimization of FTS operating conditions or
hot spot prediction.

Figure
1
Temperature comparison of simulation results and experimental data