Influence of increased gas density on hydrodynamics of bubble-column reactors

Journal Article · Sat Jan 01 00:00:00 EST 1994 · AIChE Journal (American Institute of Chemical Engineers); (United States)

DOI:https://doi.org/10.1002/aic.690400113· OSTI ID:7045722

Krishna, R; Swart, J W.A. de; Hennephof, D E; Ellenberger, J; Hoefsloot, H C.J. ^[1]

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1. Univ. of Amsterdam (Netherlands). Dept. of Chemical Engineering

A mechanistic background to the understanding of the hydrodynamics of high-pressure bubble column reactors in both the homogeneous and heterogeneous flow regimes is discussed. An important parameter determining the stability of homogeneous bubbly flow in a bubble column is shown to be the Richardson-Zaki exponent in the bubble swarm velocity relationship V[sub swarm] = [upsilon][sub [infinity]](1 [minus] [epsilon])[sup n[minus]1]. Experimental data for the bubble swarm velocity were obtained in 0.05- and 0.1-m-dia. bubble columns with various gases (helium, air, argon, sulfur hexafluoride) using water as the liquid phase. Bubble swarm velocity data show that with increasing gas density the Richardson-Zaki exponent value decreases; physically this means that increasing gas density reduces interaction between neighboring bubbles and, consequently, reduces chance of propagation of instabilities. This rationalizes the experimental observation that the influence of increased gas density [rho][sub G] is to delay the transition from homogeneous bubbly flow to churn-turbulent flow: increasing [rho][sub G], increases the regime transition velocity. A stability analysis rationalizes the observations. The hydrodynamics of bubble columns in the churn-turbulent regime is considered to be analogous to that of a bubbling gas-solid fluidized bed, and the two-phase theory of gas-solid fluid beds is extended to describing bubble columns by identifying the dilute phase as the fast-rising large bubbles and the dense phase as the liquid phase with entrained small bubbles. A simple coalescence rationalizes experimental large-bubble holdup data.

• OSTI ID: 7045722
• Journal Information: AIChE Journal (American Institute of Chemical Engineers); (United States), Vol. 40:1; ISSN 0001-1541
• Country of Publication: United States
• Language: English

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