Analysing the Operating Limits in High Gravity Equipment

Abstract

The enhancement of gas-liquid mass transfer is one of the key challenges in chemical separation processes. So far, gas-liquid contacting is predominantly performed in counter-currently operated conventional columns. However, economic and environmental constraints require continuous process improvement in terms of separation efficiency and capacity. Therefore, new column internals have been developed for conventional columns allowing for increased throughput at high performance (Spiegel and Duss, 2014). A fundamentally different approach to increase the hydraulic capacity in contacting equipment is to superimpose the gravitational force by applying a centrifugal force. To realize this approach a ring shaped packing is mounted on a rotating shaft in a so-called rotating packed bed (RPB). By application of centrifugal forces, 10-1000 times higher than the gravitational force, a capacity increase is achieved. Although the increased throughput comes at the price of an elevated pressure drop and additional power consumption of the rotating equipment, it provides a great potential for debottlenecking of existing processes or implementing gas-liquid separation technologies in space limited environment and mobile environments, like off-shore applications. Furthermore, the rotational speed acts as an additional degree of freedom for an RPB, which provides additional flexibility in terms of applicable operational conditions. Besides the height of a packing and the specific packing material, recent studies by Neumann et al. have shown that also the type of nozzle for the distribution of the liquid in the eye of the rotor is of significant importance for the specific operating limits of an RPB. Therefore, the right choice of a nozzle design can facilitate a significant higher hydraulic capacity (Neumann et al., 2017a). In the present study, we investigate the operating limits with liquid loads, at the inner cross-sectional area, up to 320 m3m2h-1 and a F-factor of 4 Pa0.5. We provide detailed insights on the relationship between the pressure drop and the rotational speed and elucidate which rotational speed is needed to achieve a certain capacity for the equipment.