Packed foams for the intensification of catalytic processes: assessment of packing efficiency and pressure drop using a combined experimental and numerical approach

Abstract

Thermally conductive packed foams have been proposed as an effective solution for the intensification of non-adiabatic catalytic processes in tubular reactors where high heat transfer rates and large catalyst inventories are necessary. Some of the open issues of this innovative solution for its scale-up to industrial process are the packing efficiency and the pressure drop. In this work, these aspects were addressed by performing both experimental activities on 3D printed foams and simulations on packed foam structures. The packing efficiency was studied by considering different spherical pellets and foam samples. The ratio between the foam window and the pellet diameter, R, was identified as the governing parameter: only pellets smaller than the window size can be packed inside the cavities of open cell foams. The packing efficiency increases with R, reaching the same asymptotic value of random packing in a tube at R > 5; for R less than 1.3 the porosity exceeds 50% and local channeling may be present. Due to commercial foam specifications, this limits the application of packed foams to processes where pellets smaller than 2 mm are employed. Pressure drop in packed foams was studied as well both by experimental tests and by numerical simulations. Despite the presence of the foam structure, pressure drops in packed foams are comparable or lower than the pressure drops in packed beds with the same pellet diameter due to the increase of the porosity inside the system. An Ergun like correlation corrected by the overall void fraction and the total wetted surface is able to describe the pressure drop in these systems with reasonable accuracy.