Axial variation of wetting efficiency and liquid-solid mass transfer in long trickle bed columns

Abstract

The wetting efficiency and solid liquid mass transfer coefficient was measured separately and simultaneously using the electrochemical cell technique while varying the superficial liquid velocity and hydrodynamic state of the column by using different pre-wetting procedures. The wetting efficiency in columns with an aspect ratio - distance from distributor divided by column diameter – of up to 33, decreased with distance from the distributor regardless of the hydrodynamic state of the column. Although the solid liquid mass transfer coefficient also decreased with an increase in axial position, this decrease was much more significant where the pre-wetting procedure that resulted in a lower overall wetting efficiency was used. When a pre-wetting procedure that resulted in a higher average wetting efficiency was used, the liquid solid mass transfer coefficient was much less dependent on liquid velocity and only a relatively small decrease with axial position was observed. The results highlight the difference in surface renewal processes that is possible between columns operated at the same conditions but under different hydrodynamic states and emphasise the importance of hydrodynamic multiplicity when liquid redistribution is considered.