Mechanical suppression of the dynamic foam head in bubble column reactors

Abstract

The necessity of suppressing foam formation arises in many industrial operations and in sewage treatment plants. Mechanical foam breakers are used for such a purpose when the use of chemical antifoams and defoaming agents is prohibited by the process. Two new foam breakers were used to control a dynamic foam head generated in a bubble column containing foamable liquid: a comb-type two-blade paddle with three slits, and a brush-type two-blade paddle with 168 needles. In comparison with more conventional foam breakers, both foam breaker designs gave significantly reduced critical speeds for foam control. Their performance was characterised under various experimental conditions including different foam-base liquid properties, gas sparger types, surfactant concentrations, and foam breaker clearances above the liquid surface level. The control of dynamic foams generated continuously in a bubble column was found to depend on the foam characteristics such as bubble size and liquid holdup, and the foamability of the base liquid. Foams generated in stirred tank reactors were found to be have different characteristics and hence different control requirements.