Gas absorption in a centrifugal reactor: hydrodynamics

• Published in: Chemical engineering science 1993, Vol.48 (14), p.2599-2608
• Main Authors: Roizard, C., Mokrani, F., Le Gall, H., Midoux, N.
• Format: Article
• Language: English
• Subjects: Absorption, stripping; Applied sciences; Chemical engineering; Exact sciences and technology
• ISSN: 0009-2509; 1873-4405
• DOI: 10.1016/0009-2509(93)80270-Z

For the removal of SO 2 and/or NO x using an oxidizing liquid solution, absorbers with a high mass transfer efficiency are required. Here, a centrifugal gas—liquid absorber has been designed and studied; the chosen device is a rotor with blades which induce the formation of a thin liquid film on the reactor wall. The operating parameters that can be varied are the rotation speed, the back pressure at the liquid outlet and the gas and liquid flow rates. Three distinct flow regimes can be visualized, depending on the values of the parameters. The hydrodynamic regimes vary from thin liquid film containing dispersed gas bubbles with large gas holdup to thick films containing virtually no gas. Residence time distributions of the liquid phase allow to measure the liquid film volume (liquid holdup) in the reactor and the dispersion coefficient. The liquid volume increases with back pressure but decreases with increasing rotation speed. The Peclet number decreases with increasing back pressure. In the investigated range, no influence of the liquid and gas flow rates was found on either of the above two factors. Furthermore, the liquid volume and the Peclet number can easily be correlated to the Euler number, which is the ratio of the relative back pressure to the centrifugal pressure. A hydrodynamic model based on a pressure balance in the reactor leads to the expression of the liquid film thickness along the height of the blade as a function of Euler number and Δ p*, the dimensionless ratio of the relative back pressure to the gravity. These two dimensionless numbers depend only on the operating parameters. The angular liquid velocity was supposed to be proportional to the rotor angular velocity: the shift coefficient k is determined from the experimental values of the liquid holdup. Results show that k can be correlated to the Euler number. Using these results, calculated liquid film thickness profiles are presented and discussed.