Hydrodynamic Characteristics Effect of Foam Control in a Three-Phase Fluidized Bed Column

Abstract

The present work was devoted to study the effect of operating parameters (e.g., superficial gas and liquid velocities, size of solid particles, volume percentage of particles loaded in column and type of particles) on foams, and to investigate the process of foam suppression.

         The experimental apparatus was operated in continuous mode for the two phases (i.e. air and a solution of aqueous anionic surfactant). Sands which were considered as hydrophilic behavior particles were used as solid phase. A specific surface treatment was performed on hydrophilic sands particles to transfer it into hydrophobic one. These two versions of sands were used in the experimental setup respectively to study their effect on suppression of foams. The average gas holdup for the entire column was measured by means of the local gas holdup which was computed from the pressure difference in each segment of the column. Local solid concentration along the column was measured experimentally by analyzing the samples of mixture drawn from the sampling ports. From the present work it was found that: Flow regimes of multiphase system could be easily determined by utilizing local gas holdup profile measured by pressure drop transducer method. The transition from the homogenous to heterogeneous regime was advanced, from u_g=4 to 2cm/s with increasing solid concentration from 10 to 20%v and decreasing average particle diameter from d_p=(0.8) to (0.25) mm.

         When a mixture of water/surfactant was employed in the bubble column, foam could be present depending on the input operating parameters. The fluid mechanism of foam suppression with hydrophilic particles was enhanced by a direct attack on the foam by hydrophobic particles (i.e. hydrophobic particles were more effective in retaining liquid–destroying foam than the hydrophilic particles). It was found that hydrophobic particles of 0.25 mm average diameter and 10%v loading in the reactor could reduce foaminess fraction from 0.85 to 0.15 if the liquid velocity was 0.3 cm/s. The foaminess fraction could be reduced to 0.0 if the liquid velocity increased to 0.4 cm/s. The results of this study may have abroad applications in petroleum and petrochemical industries where liquid hydrocarbons are processed.