Miniaturisation of the toroidal fluidization concept using 3D printing

Abstract We used the stereolithography printing technique to fabricate a toroidal fluidized bed at the smallest scale ever achieved (50 mm diameter with 10 mm annular width). In toroidal fluidization, most of the kinetic energy of the fluidizing gas is used to induce swirling of the particle bed meaning higher gas velocities can be used without entrainment. The end-goal of this research is to use this ‘mesoscale-TORBED’ for screening adsorbents for CO2 capture, where the intensified heat/mass transfer rates can potentially minimise the troublesome scalability issues encountered in standard packed beds, a consequence of gradient effects. Here, we have performed a comprehensive parametric study to understand the influence of bed loading, gas volumetric flow rate, gas temperature and gas humidity on the swirling bed formations of activated carbon pellets in order to identify appropriate conditions for sorbent screening. We show that desirable ‘uniform packing’ occurs across a broad range of operating conditions and identify the lower bed loading limit as 1200 mg. Other observed bed formations included collapsed, maldistributed and entrained states that caused gas bypassing of the particle bed. At the lowest air flow rate studied (27 L/min), the bed was either in the collapsed state or not swirling at all, whilst swirling was readily observed at the intermediate and high air flow rates (35.5 L/min and 44 L/min respectively). Humidity and air temperature had minimal influence over the flow patterns.