In a stirred-tank reactor (STR), a comparison of the performance of mechanical foambreakers: a six-blade turbine (F-B), a six-blade vaned disk (V-D), a two-blade paddle (T-P), a conical rotor (C-R), a fluid-impact dispersion apparatus (FIDA) and a rotating disk mechanical foam-breaker (MFRD) was carried out using defined foaming media. The foam-breaking ranges (relative to the gas superficial velocity, U g ) of the T-P, C-R and FIDA were inferior to that of the F-B, V-D and MFRD. The power consumption, P kc , for foam-breaking in the MFRD was the lowest among the F-B, V-D and MFRD. Operation of the F-B and V-D in the STR caused a considerable amount of liquid droplets from the collapsed foam to be entrained with the exhaust air.

No abstract

The foam-breaking characteristics of rotating-disk mechanical foam-breakers (MFRDs) ®tted to stirred-tank reactors (STRs) containing various foaming liquids were evaluated. The critical disk rotational speed, N c , required for foam-breaking and the liquid hold-up, f L , in ascending foam re¯ected, respectively, the foam-breaking behaviour of MFRDs and the foaming behaviour of STRs. Empirical equations for the prediction of N c and f L , which can be applied independently of the type, concentration and temperature of foaming liquid, were obtained. The foam-breaking power, P kc , of MFRDs was also clari®ed in relation to the level of f L which is related to the dif®culty or ease of mechanical foam-breaking.

Rotating‐disk mechanical foam‐breakers (MFRDs) were applied to the control of foaming in bubble column (BC) reactors containing complex solutions and biological media. The foaming behaviour of BCs and the foam‐breaking behaviour of MFRDs fitted to BCs were evaluated respectively from the changes in the liquid hold‐up in ascending foam, ϕb, and the required critical disk rotational speed, Nc, for foam‐breaking. The differences in ϕb and Nc, reflecting the difficulty or ease of foam‐breaking among the liquids, correlated well with differences in the foaming characteristic term, FCT, of respective liquids, which could be determined on the basis of the results measured in the experimental small foaming apparatus which were different from those measured in the gas‐bubbling apparatus employed in practice. The usefulness of the empirical correlations for the prediction of ϕb and Nc, which can be applied independently of the type and concentration of foaming liquid or their physical properties, was also demonstrated.

No abstract