Impact of Number of Rotors in Rotating Packed Beds on Separation Performance in Distillation

Abstract

Different configurations of a rotating packed bed (RPB) were used in a distillation study to comprehend the impact of the number of rotors on the separation performance of ethanol/1-propanol distillation at total reflux and atmospheric pressure. The separation performance of a single-rotor RPB (1R-RPB) was compared with that of a two-rotor RPB (2R-RPB). To achieve a uniform liquid distribution in the lower rotor of the 2R-RPB, a liquid collector and a rotating baffle distributor (RBD) were installed. The rotational speed (n rot ) was varied between 300 and 1200 rpm, and two different F-factors were investigated (F G = 1.3 Pa 0.5 and F G = 2.1 Pa 0.5 ). The pressure drop of each rotor in the different setups was nearly equal. Thus, neither the liquid collector, nor the RBD, nor the intermediate floor contributed significantly to the total pressure drop of the RPB. The separation performance of the lower rotor of the 2R-RPB was in fair agreement with the separation performance of the 1R-RPB at F G = 1.3 Pa 0.5 for all investigated n rot . This demonstrates that the separation performance in a 2R-RPB can ideally be twice as high as that of the 1R-RPB. However, there are separation performance losses compared to the ideal case. At F G = 2.1 Pa 0.5 and n rot = 900 rpm, the lower rotor of the 2R-RPB shows a separation performance loss of 36% compared to the 1R-RPB, which can be compensated for by increasing n rot to 1200 rpm. Therefore, this study provides a promising concept for numbering up rotors in RPB machines to enable separation tasks that could not be achieved in 1R-RPBs due to the limited separation performance.

Distributor Effects on Liquid Hold-Up in Rotating Packed Beds

“…Contrary to liquid injection with SPFJ nozzles, the liquid is specifically accelerated at each new rotor stage using RBDs, which guarantee defined boundary conditions at each new rotor stage in terms of liquid distribution (Figure ). Therefore, an RBD does not necessarily require such central liquid inlet as in single-rotor RPBs, which was recently demonstrated in a multirotor RPB distillation study where the RBD was applied in the lower rotor and upper rotor . The angle of the droplet breakup (α) can be determined by connecting the outer edge of the baffle with the entry of liquid toward the packing (see Figure a).…”

Improved Mass-Transfer Model for Distillation in a Pilot-Scale Concentric Ring Rotating Bed as a Rotating Packed Bed

“…Total reflux distillation experiments showed that the distributor led to a higher separation efficiency, compared to the conventional nozzle liquid distributor. Pyka et al 12 compared the pressure drop and the separation performance of a single-rotor RPB with those of a two-rotor RPB at the same operating conditions. Results showed that the pressure drop as well as the separation performance in the two-rotor RPB could ideally be twice as high as those of the single-rotor RPB.…”