STUDIES OF AN INDEPENDENTLY-DRIVEN, DUAL IMPELLER PROTOFERMENTER WITHAND WITHOUT A DRAFT TUBE - POWER AND HOLD-UP

An independently-driven, dual impeller system in a transparent vessel of diameter 0.75 m and a liquid height with an aspect ratio of 2 has b een studied, with and without a draft tube installed. A Rushton turbin e and a Scaba 3SHP1 axial flow impeller were employed with water as th e fluid. The power drawn by each impeller was measured independently, both under unaerated and aerated conditions. The hold-up was also meas ured and both parameters are related to the observed hydrodynamics of the two-phase flow associated with each combination of impellers. Over all, the dual impeller combination with the two being driven at differ ent speeds in the presence of the draft tube, gave the most stable ope rating conditions and the highest hold-up when compared at equivalent aeration and energy dissipation rates.