Mechanical control of foaming in tower reactors

Abstract

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.

Mechanical control of foaming in stirred‐tank reactors

“…Liquid hold‐up in foamate (ϕ t ), rate of liquid drainage from foam ( v ), foam velocity ( u f ) and foam size ( d f ) were newly measured at 303 and 313 K under constant air‐bubbling condition. The values of these parameters are summarized in Table 2 together with those at 293 K obtained in previous works 12. 15 The liquid hold‐up in foam (ϕ f ) in the column, defined by eqn 1 15 as a function of ϕ t , v and u f , was then evaluated.…”

“…Previously,10 a mechanical foam‐breaker with rotating disk (MFRD) was constructed that facilitated foam‐breaking action by the effect of the impact between the liquid drops dispersed from the disk and the ascending foam. The performance and operational characteristics of MFRDs were assessed for tower reactors, ie bubble columns (BCs), containing various foaming liquids 11–14. Through these studies, the MFRD proved to be useful in controlling foaming in BCs without antifoam agents.…”

Performance characteristics of mechanical foam‐breakers fitted to a stirred‐tank reactor

“…In the high N i range (>25.00 s À1 ), the increased foaming capacity due to an increase in N i may be balanced by the decreased foaming intensity due to the foam entrainment. 19 Correlations of N c were carried out for the F-B and V-D systems that permitted successful foam-breaking at all the operating conditions, using parameters such as U g , the Froude number (Fr) i of the impeller and the foaming characteristic term (F CT ) 16 Figure 5 shows the typical distribution of (f L ) L , which is plotted against the radial distance R from the wall. The MFRD 19 is also shown.…”

Improvement of foam breaking and oxygen-transfer performance in a stirred-tank fermenter

“…Therefore, the improved foam-breaking performance with increasing D F is attributable to the increased suction force caused by increased D F . Because the rotational speed of the agitation impeller was increased, thereby increasing the foaming capacity, the foam tended to break up less [14,20]. On the other hand, the foam-breaking performance of the foam-breaking impeller was enhanced by the increased suction force created by the increased rotational speed.…”