Interrelation among Liquid Velocity, Impeller Speed and Gas Flow Rate in the Stirred Airlift Reactor

Abstract

We investigate the liquid circulation velocity in the draft-tube airlift reactor, with mechanical agitation in the internal column as a riser, at the impeller speed of up to 40 s–1. An influence of the gas flow rate and the stirrer speed on the riser and downcomer gas hold-up difference and on the liquid circulation velocity is also investigated. The character of the liquid circulation velocity changes depends on the relation between the gas flow rate and the impeller speed. A monotonic increase of the liquid circulation velocity with an increase of the gas velocity is observed at the impeller speed of lower than 15 s–1. A distinct decrease of the liquid velocity is found at higher impeller speeds and at low gas velocities. The decrease is larger for higher impeller speeds. We observe the minimum on the curve of the liquid velocity dependence on the gas velocity followed by the monotonic increase of the liquid velocity with an increase of the gas flow velocity. The minimum of the liquid circulation velocity appears if the ratio of the gas flow number to the impeller speed is about 0.0006. The minima are shifted towards the higher gas velocities at higher impeller speeds. An experimental equation for the prediction of the liquid circulation velocity in the stirred airlift reactor is presented.