Advanced absorption model of rotating packed beds: Mass transfer in packing and cavity zone

A comprehensive absorption model was developed for a counter-current rotating packed bed apparatus. The model describes the mass transfer phenomena occurring in both the packing zone and the cavity zone. It was shown that the droplet size distribution follows log-normal function and is dependent mainly on the size and rotational speed of the packing. According to their characteristics, primary droplets present in the cavity zone were divided into four classes: pseudo-mothers, non-splashing mothers, splashing mothers and daughters. The entrained droplets (pseudo-mothers and daughters) follow the gas back towards the rotor and are partially deposed along the way due to gas phase turbulence, which is described by the proposed return coefficient. It was determined that mass transfer efficiency of the cavity zone depends mostly on size and rotational speed of the packing (primary droplet size and velocity distribution, as well as tangential acceleration of the gas), curvatures of packing and casing (radial component of mother droplet velocity), and gas flow rate (residence time of entrained droplets). The model has been successfully validated with experimental data within ±25 % relative error range. Simulations show that decrease in packing zone size may be beneficial to the overall process, e.g. at casing radius of 320 mm, reduction of the packing radius from 200 mm to 150 mm leads to over 15 % increase in CO2 absorption efficiency. This work was supported by the joint Polish-Czech project: no. UMO-2020/39/I/ST8/01381 financed by the National Science Centre, Poland, and no. GA 21-45227L financed by the Czech Science Foundation.