Effect of liquid-phase surface tension on hydrodynamics of a three-phase airlift reactor with an enlarged degassing zone

Abstract

The effect of the addition of ethanol (10 g/l) to the liquid-phase on gas and solids holdup, circulation and mixing times and interstitial liquid velocity in a three- phase airlift reactor was investigated. The airlift reactor (60 l) is of the concentric draught-tube type with an en- larged degassing zone. Ca-alginate beads were used as solid-phase and airflow rate (from 1.9 to 90.2 l/min) and solids loading (0-30% (v/v)) were manipulated. Riser and downcomer gas holdup were found to increase with the addition of ethanol, leading to a decrease on the relative solids holdup. The presence of ethanol seems to have no influence on the circulation time. On the other hand, mixing time variation depends on the solids loading and airflow rate. Riser and downcomer interstitial liquid ve- locity are lower for ethanol solution than for water. List of symbols Ad downcomer cross-section area (m) Ar riser cross-section area (m) d vertical distance between two points of the riser and of the downcomer (m) H1)H2 pressure difference between two points of the riser and of the downcomer (cmH2O) tc circulation time (s) tm mixing time (s) uld downcomer interstitial liquid velocity (m/s) uli interstitial liquid velocity in section i (m/s) ulr riser interstitial liquid velocity (m/s) vgr riser superficial gas velocity (m/s) Vs solids volume measured in each sample (l) VT sample total volume (l) Dt time required by the tracer to travel between the two acquisition points in the riser and in the downcomer (s) egd downcomer gas holdup