Gas Hold-up in Three-phase Multiimpeller Stirred Reactor

Abstract

Applications of three-phase bubble columns are increasing in chemical and biotechnical processes. Frequently, these reactors are operated at high solid and gas holdups. Electrodiffusion measurement (EDM) results are presented for local liquid flow velocities under such practically relevant conditions and compared to CFD modeling results. A multifluid model using the k-HH turbulence model and special terms for the direct momentum exchange between gas and solid phase has been implemented using the CFX-4.3 solver. Parabolic radial profiles of axial liquid velocity are obtained with measurements as well as with computations; the influence of increasing superficial gas velocity on liquid circulation is qualitatively well captured by the modelling calculations. 508* Gas Hold-up in Three-phase Multiimpeller Stirred Reactor M a c h o n , V . J a h o d a , M . V e v e r k a , P . M a j i r o v a , HThe gas hold-up has been measured in the tank stirred with two pitch blade turbines downward pumping effect. The used gas was air and liquid charge were suspensions of glass beads of mean diameter 0.14 mm and/or polyvinyl particles 0.94 mm. The concentration was up to 30 % w/w (glass beads) and up to 10 % w/w (polyvinyl particles). The liquid was either water (coalescing system), 0.5 M solution sodium sulphate and 0.1 M ethanol solution (non-coalescing systems). In agreement with literature the higher gas hold-up has been found in non-coalescing systems. The presence of solid particles had ambiguous effect on hold-up: in water was not observed the influence of solids, in sulphate and ethanol solutions the gas hold-up decreased with the concentration of solid particles. The data has been correlated according the equation in which stirred speed and gas flow rates occur. 509* Local Effects of Hydrodynamics andMass Transfer in Multiphase Flows M . S c h l u È t e r S . J o h n S . S c h e i d H . P a r c h m a n n O . B o r k P r o f . D r . N . R a È b i g e r