Effect of gas density on large-bubble holdup in bubble column reactors

Abstract

Increased system pressure or gas density changes the hydrodynamics in gas-liquid bubble columns. This has important consequences for the design of bubble column reactors, since the hydrodynamics at commercial operating conditions can differ considerably from the situation in cold flow experiments. Since empirical correlations have limited applicability, it is of importance to understand the physics of the effect of increased gas density, at least up to a point where still reasonable predictions about the gas fraction can be made. In this article we explain the effect of gas density on largebubble holdup by considering the effect of gas density on the rise velocity of large bubbles. We apply the Kelvin-Helmholtz theory to predict this influence on the large-bubble rise velocity. The theoretical dependence derived from this theory is checked by analyzing experimental gas-fraction data, acquired in a 0.15-m-ID column at system pressures up to 1.3 MPa.