The Fischer-Tropsch synthesis (FTS) has been recognized as a key technology to convert natural gas reservoirs into synthetic liquid fuels and valuable chemicals. Consequently, intensification of Fischer-Tropsch fixed-bed reactors has been gaining considerable attention recently. This is due to the necessity of exploiting both associated and remote natural gas fields, as well as biomass, to produce liquid fuels, which requires scaling down the conventional packed-bed multi-tubular reactors to modular compact units. This approach nonetheless suffers from a critical drawback regarding heat transfer, due to the strong exothermicity and the high temperature sensitivity of the Fischer-Tropsch catalytic reaction. In fact, heat transfer remains the key challenge for the intensification of the FTS in compact fixed-bed reactors. In a recent publication by the same authors here, it was shown that the possibility to overcome these heat transfer limitations is through the adoption of the conductive packed-foam reactor technology. Along these lines, periodic open cellular structures (POCS) have been recently reported. POCs have been shown to significantly outperform randomly packed-beds owing to the considerable contribution of the conductive heat transfer mechanism in cellular structures. Regardless, their use in FTS has not been examined experimentally so far.
To address this, Politecnico di Milano Italian researchers: Dr. Laura Fratalocchi, Dr. Gianpiero Groppi, Dr. Carlo Giorgio Visconti, Dr. Luca Lietti and led by Professor Enrico Tronconi, demonstrated experimentally at lab scale, for the first time, that the heat transport performances of a FTS fixed-bed reactor could be enhanced through the adoption of a periodic open cellular structure made of aluminum. Their goal was to reveal the additional benefits that could be ripped by adopting internals based on innovative conductive cellular structures with an engineered flexible design. Their work is currently published in Chemical Engineering Journal.
In their approach, the researchers first prepared and characterized the catalyst they were to use in their experiment. Next, POCS samples to be used in the experiment were manufactured by 3D printing based on the Selective Laser Melting technology and using AlSi7Mg0.6 as starting metal powder. Catalytic tests and kinetic measurements in the Packed-POCS reactor were then carried out. Lastly, the thermal behavior of the packed-POCS reactor was evaluated.
The authors reported that, for the first time, the heat exchange in FTS fixed-bed reactors could be enhanced thanks to the adoption of highly conductive internals based on periodic open cellular structures. In fact, their data clearly indicated that the adoption of a conductive packed POCS enabled them operate the FTS reactor quasi-isothermally even under very severe conditions. Interestingly, during testing the packed-POCS reached extreme operative conditions that could not be accessed using the conventional randomly packed fixed-bed reactor, even if operated under milder conditions.
In summary, the study demonstrated that the adoption of conductive cellular structures packed with catalyst particles enabled one to extend the feasible range of kinetic investigations for lab-scale studies of strongly exo- (but also possibly endo-) thermic catalytic reactions. Remarkably, the heat transfer of the packed-POCS reactor outperformed both packed-bed and packed-foam reactors, granting smaller radial temperature gradients in the catalytic bed, as well as smaller temperature differences at the reactor wall, with larger volumetric power releases. In a statement to Advances in Engineering, Professor Enrico Tronconi further clarified that the strengths of the packed-POCS reactor configuration were its regular geometry, which enhances the effective radial thermal conductivity, and the improved contact between the structure and the reactor wall, which governs the limiting wall heat transfer coefficient.
This project has received funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (grant agreement No 694910 -‘INTENT’)”
Laura Fratalocchi, Gianpiero Groppi, Carlo Giorgio Visconti, Luca Lietti, Enrico Tronconi. Adoption of 3D printed highly conductive periodic open cellular structures as an effective solution to enhance the heat transfer performances of compact Fischer-Tropsch fixed-bed reactors. Chemical Engineering Journal, volume 386 (2020) 123988.