Effect Of Nozzle Diameters On The Distribution Of Bubbles And Mass Transfer In Bubble Columns

Bubble column reactors are widely used in gas-liquid reaction process, such as absorption, catalytic slurry reaction, bio-reactions, etc. They are easy operated and economic in cost. In a bubble column, gas distributors play a key role in the bubble distribution. The orifice diameter of the distributor directly influences the gas-liquid interface area and mass transfer efficiency of the column. So it's necessary to research the effect of nozzle diameters on the distribution of bubbles and mass transfer in bubble columns.Considering the formation of bubbles at the nozzle, coalescence and break-up process in the columns were analyzed. A PBE (Population Balance Equations) model was developed to describe the time dependence of gas number density. It can be used to evaluate the effect of nozzle diameter on bubbles distribution. Using on-line monitoring technology, effect of the nozzle diameters on, liquid volume mass transfer coefficient, and its axial distribution were studied.In this article, following conclusions are made: (1) the properties of liquid phase have the dominant effects on the bubble formation and distribution, especially the latter. (2) With increasing of superficial gas velocity, both the coalescence and breakage of bubbles become intensive. To large bubbles, the breakage process is dominant, and the breakage is unequal. (3) The maximum stable diameter,, has important effect on bubbles distribution. Bubbles having diameters less than, can go through the columns stably. On the other hand, bubbles having diameters large than, will experience a fast breakage process. To unstable bubbles, an equilibrium distribution is reached at the distance 20-25cm from the nozzle. Nozzle diameters have little effect on the equilibrium distributions of bubbles, so do to. (4) There is an axial distribution of in bubble columns, at the distance range 40-60cm from the nozzle, a maximum is reached. Out of the upper limit, a less appears, and out of the lower limit, a least exists. (5) The liquid volume mass transfer coefficient () of bubble columns can be expressed by . The exponent (n), which has a value of about 1 (0.78-1.06) and is mainly influenced by system properties, can be hardly improved. The coefficient, b, which indicates the importance of gas distributor on mass transfer and falls in the range of 0.460-1.445, can be improved by more effective gas distributors.