Mixing studies in external-loop airlift reactors

The mixing behaviour of the liquid phase in two external-loop airlift reactors of laboratory and pilot scale, in terms of the mixing time and axial dispersion, was investigated. The mixing parameters were determined from the output curves to an initial Dirac pulse, using the classical tracer response technique, and analysed in relation to operating and geometrical parameters, such as v(sGR),A(D)/A(R),H-d and D-R. Mixing in the external-loop airlift reactors under investigation was essentially correlated with the liquid circulation velocity. The specific sections of the airlift reactor have different mixing behaviour, so that the riser and downcomer can be analysed as plug flow with axial dispersion, whereas the top section approaches ideal mixing behaviour. A simple correlation between the specific mixing time and the operating and geometrical parameters was developed which can be used for design and scale-up purposes. (C) 1997 Elsevier Science S.A.