(193d) Development of Packing Design for Distillation in Rotating Packed Beds

Fluid separations performed in conventional columns are limited by the gravitational field in terms of applicable liquid and vapor loads. Difficult separation processes or high throughputs often result in large column dimensions and high investment cost. However, flexible and modular equipment is of growing importance for meeting challenges in the chemical industry. Rotating packed beds (RPBs) are a promising example of flexible and modular contacting equipment employing HiGee (high gravity) technology. The centrifugal force imposed by the rotation of an annular shaped packed bed located in a stationary casing superimposes the gravitational force and results in reduced film thickness and enhanced mass transfer. This allows the implementation of comparable separation performance in smaller equipment with a higher capacity compared to a conventional column [1].

So far, the range of available packings for RPBs is rather limited and mainly wire mesh and metal foams are employed for various separation processes. For these isotropic packings, the cross-sectional area and the gas capacity factor, commonly represented by the F-factor, is continuously changing along with the radius of the packing. As recent gamma-ray tomography showed, a significant decrease of liquid hold-up with increasing radial length of the packing and rotational speed [2]. These variations decrease the overall performance of the packing. To overcome these limitations a newly developed ZickZack packing, like the concept of a tray-like structure in rotating zigzag beds (RZB), was developed. Contrary to RZB, the ZickZack packing is a regular structure, which is placed within the rotor of an RPB.

The current study represents a comparison of the separation efficiency and the pressure drop of conventional isotropic packings and the ZickZack packing in an RPB. Separation of an alcohol-water mixture under total reflux distillation operation at atmospheric pressure is performed. The experimental results show that the ZickZack packing not only improves the separation efficiency in the packing but also improves the overall separation performance of the RPB without additional pressure loss within the investigated vapor and liquid loads.

References

[1] Neumann et. al., Chem. Eng. Res. Des., 2018, 134, p. 443 – 462.

[2] Groß et. al., Proceedings of 9th World Congress on Industrial Process Tomography, 2018, Bath, UK, p. 831 – 838.

The research is done in cooperation with the Institute of Sustainable Process Technology (ISPT) in the framework of the project ImPaCCt (Improved Process Performance by Process Intensification in Centrifugal Contactors).