Mass transfer estimation for bubble column scale up

Abstract

The productivity of a bubble column reactor (BCR) critically depends upon gas-liquid mass transfer coefficient, kLa. The prediction of kLa as function of design and operating conditions is central to BCR scale up. A large number of researchers have successfully characterized kLa experimentally in terms of superficial gas velocity, Usg using the power law relation kLa=αUsgβ, with α,β as fit parameters. We probe the applicability of such correlations to the design of a scaled up BCR, which differs from laboratory BCR in two important aspects: (i) the scale of operation, which can be O(102-103) times larger, and (ii) the type of sparger used. To this end, experiments were performed with air and water in a pilot scale (DC=1.6 m diameter) BCR using a coarse bubble sparger. We found that the existing correlations do, indeed, describe kLa over a wide range of BCR sizes, suggesting that these correlations are fairly scale insensitive. However, the correlations provide no means to capture the role of sparger explicitly. We cast our experimental kLa values in terms of a mass transfer efficiency and independently recover the power law relation with β=1. We suggest that the role of sparger design can be incorporated in the definition of α through the well-documented sparger efficiency factors. The α and β estimates thus obtained are in good agreement with the literature.