Aeration and Mixing in Loop Reactors Equipped With Fine Bubble Diffusers and Slow Speed Mixers: A Full Scale Study

Mixing and aeration characteristics obtained on three full scale loop reactors for 28 configurations (different mixers' location and rotation speed, air flow rates and diffuser grids' location) were analyzed. The propellers' thrust was measured in situ. Observed values vary with the tank geometry, the location of the mixers and the induced axial velocity. in situ thrust values are lower than the nominal ones obtained during shop tests, by 10 to 30 %. For the nominal rotation speed of the propellers, observed thrust-to-power ratios are comprised between 685 and 875 N kW−1. In agreement with previous results, an increase in the oxygen transfer rate with the axial velocity was observed, due to a partial neutralization of the spiral flows formed at the edge of the aerated zones. Aeration efficiency is not decreased, as the additional power consumption due to mixing is offset by the oxygen transfer enhancement. SAE values are comprised between 2.0 and 2.6 kg O2 kWh−1. Such on site results are especially important to be used as input and output data in CFD models.