Mechanical control of foaming in stirred‐tank reactors

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.

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

“…19 The tendency of changing P kc with increasing N i was similar to that of changing N c or W c and f L discussed above. P kc in the C-R exhibits the best performance.…”

“…The performance and operational characteristics of MFRDs were also assessed for stirred-tank reactors (STRs), containing various foaming liquids. 19 The MFRD proved to be useful in controlling foaming in STRs without antifoam agents. Here, five typical foam-breakers which are often found in commercial laboratory-STRs are compared with the MFRD.…”

“…When N i exceeds 11.67 s À1 , the impeller may act to entrain the foam from the headspace of the STR to the aerated liquid surface, resulting in a decrease in ascending velocity of the foam. 19 The foam is, consequently, more easily broken due to the decreased foaming intensity. 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.…”

“…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.…”

Performance Characteristics of a Stirred-Tank Reactor with a Mechanical Foam-Breaker Utilizing Shear Force

“…In most of the proposed mechanical foam-breakers, the resultant secondary foams are returned to the area of primary foam generation and are thus accumulated in the reactor over its long lifetime. Examples include mechanical foam-breakers with rotating installations such as turbines, vaned disks, and paddles (Ng and Gutierrez, 1977;Deshpande and Barigou, 1999;Takesono et al, 2001Takesono et al, , 2002. In such devices, persistent secondary foams recirculate into the foam-breaker, but cannot be broken twice by the foam-breaker.…”