Investigating Microchannel Reactors for Fischer-Tropsch Synthesis

Microchannel reactors (MCRs) exemplify significant miniaturization of the physical dimensions and process intensification when compared with conventional industrial reactors, allowing for linear scaleup, flexible manipulations, and substantial capital cost reductions. MCRs have promising applications in Gas-to-Liquid (GTL) technologies, such as the Fischer-Tropsch (F-T) synthesis, particularly for monetizing small onshore and offshore gas fields, which is economically unfeasible with other conventional industrial F-T technologies. Even though MCRs were proposed for commercial implementations and demonstration plans have already been built, adequate literature publications on the use of MCRs in F-T synthesis is scanty and to the best of our knowledge many details concerning the hydrodynamics, mass transfer, heat transfer, and reactor performance are not available. \ud The overall objective of this study is to investigate the performance and the flow distribution of a MCR, using one-dimensional (1-D) and Computational Fluid Dynamics (CFD) models. A MCR consisting of 50 channels, each packed with 100-micron cobalt catalyst, operating under the low temperature F-T synthesis (500 K and 25 bar) was used to study the reactor performance. The inlet flow distribution was investigated using another CFD model with air at 298 K and 1.01325 bar. A 50-channel MCR was used in this investigation. The modeling results led to the following conclusions:\ud 1. The 1-D model systematically predicted steeper hydrocarbon flow rate profiles when compared with those of the CFD model, however, both models converge to the same values at the channel outlet. \ud 2. For one channel of the MCR, both the 1-D and CFD models indicated that increasing the H2/CO ratio in the feed increased CO conversion, C5+ yield, pressure drop, F-T reaction rate, and the heat transfer requirements. Increasing the inlet syngas velocity decreased CO conversion and increased the pressure drop. Also, increasing temperature, increased the F-T reaction rate, CO conversion and the C5+ yield, and decreased the pressure drop. Furthermore, under the conditions investigated, the F-T process in the MCR used was kinetically-controlled.\ud 3. The CFD model used to investigate the flow distribution in the MCR showed that using a flow distributor resulted in a homogenous flow distribution and eliminated the strong gas recirculation