Hydrodynamics and mass transfer in a three-phase air-lift reactor.

The hydrodynamics and mass transfer characteristics were studied in a rectangular three phase air lift reactor. Solid phase characteristics were varied and included wettable and nonwettable solids, with solid densities ranging from less dense to more dense than the liquid phase. The measured overall gas/liquid mass transfer coefficient was found to decrease with increasing solids loading, for all solids investigated. The extent of the decrease was small for the wettable solids, however, there was a significant decrease in mass transfer in the presence of nonwettable solids. It is shown that solids hold up in the riser and downcomer is not equal and will be a function of the terminal particle velocity and liquid velocity. Liquid velocities were slightly reduced in the presence of the solid phase. The effect is more pronounced at low power inputs. Different approaches for analyzing three phase air lift systems are discussed. Use of different approaches to system analysis may explain part of the variation in the studies found in the literature for three phase air lift systems.