A Comprehensive Numerical Simulation of a Low-Temperature Fischer-Tropsch Synthesis in a Fixed Bed Reactor in Trickle Flow Regime

Gas to liquid (GTL) process involves heterogeneous catalytic chemical reactions that convert synthesis gas to hydrocarbons and water vapor. Fischer-Tropsch synthesis, as the heart of the process, is a three-phase chemical phenomenon that includes gaseous phase-synthesis gas, light hydrocarbons and water vapor, liquid phase–heavy hydrocarbons, solid phase-catalyst and wax products. The presence of liquid phase in catalytic packed bed in LTFT synthesis causes mass transfer restrictions and affects the reaction conversion. In this work, a numerical simulation of the LTFT fixed bed reactor in trickle flow regime has been accomplished using numerical computation codes to understand the impact of liquid phase on the reactor performance. For this purpose, we have developed an axisymmetric two-dimensional multiphase heterogeneous model where syngas, containing carbon monoxide and hydrogen, can be transferred into the liquid phase. The reactor consists of a shell and tube that filled with a spherical cobalt catalyst. Reaction conditions are as follows: a wall temperature of 473 K, a pressure of 20 bars, and a gas hour space velocity (GHSV) of 111Nml.gcat^ −1 . h^−1. Numerical simulation results proved the negative impact of liquid presence on the reaction conversion. Model predictions were examined against reported experimental and numerical pseudo-homogeneous model, and it was found that applying the heterogeneous, instead of pseudo-homogeneous, model decreases clearly the deviation of numerical results from experimental data. Thus, assuming the single-phase flow in LTFT synthesis is not always true.