Hydrodynamics of semibatch slurry bubble columns with polymer solutions

In this work we perform an experimental study of the hydrodynamics of semibatch slurry bubble columns in which the liquid phase is a solution of a high molecular weight hydrolyzed polyacrylamide. Experiments were conducted in bubble columns with two different diameters (10 and 29 cm.) In gas-liquid operation, the gas holdup decreases as the polymer concentration increases due to the formation of large stable bubbles. In the presence of high solids concentration, this trend is reversed in the larger column due to an increase in the number of small bubbles and an appreciable increase in the residence times of the large bubbles brought about by an increase in slurry circulation. The distribution of solid phase becomes more uniform as the polymer concentration increases. This trend is quantified by means of the application of a modified form of the sedimentation-dispersion model. The macromolecular conformation of the polymer in solution is altered by adding NaCl, whose positive ions screen negative charges in the polymer molecule producing a contraction of the coil. At the concentration levels used in this work, the addition of salt decreases the ability of the polymer to produce a more uniform solids distribution.