Bioreactors have recently become a technology of interest for conversion of hydrocarbon gases to liquid fuels. Economic viability of this process requires exceptionally low reactor costs and high production rates. Therefore development of ambient pressure bioreactors with a fast gas-liquid mass transfer coefficient (k
La) and low energy consumption is desired. One strategy to achieve this goal is to increase interfacial area density, a, to >3000 m
2/m
3, with minimal use of energy. We compare published reactor technology with our own measurements from a new reactor design that utilizes downward-bubble flow away from an array of micro-jets (Li 2014). This advanced design achieves more efficient k
La per power expenditure while operating at higher k
La. We present measurements from four reactor heights (height-to-diameter ratios of 12, 9, 6 and 3) of k
L, total interfacial area a, liquid residence time distribution, energy consumption, turbulent hydrodynamics, bubble breakup size, bubble size distribution, surface tension, . A physical model for predicting k
L and is validated, and suggests that k
L is governed by different hydrodynamics at different locations below the micro-jet array: 1) “entrance effects†due to Higbie (1935) penetration dominate at short distances, 2) turbulence (Calderbank & Moo-Young 1961) dominates at intermediate distances, and finally 3) terminal rise velocity (Clift 1978) dominates at large distances. Recent advances in the understanding of molecular and hydrodynamic forces are applied to our data, including the effects of sodium dodecyl sulfate (SDS) and potassium chloride (KCl). We find that surface tension is not the leading physical force to control bubble breakage and coalescence rate. We use recent literature to make calculations of the leading intra-molecular and hydrodynamic forces. The experimental behavior of the bubbles is well explained by the sum of molecular and hydrodynamic forces. Improvements are suggested for predictions of bubble size in gas-liquid dispersions in agitated vessels, which classically assume that surface tension is the connection between molecular additives and macroscopic bubble behavior (Akita Yoshida 1973, Liao 2010).
References:
Li, X. (2014), United States Patent 20140212937A1, System and method for improved gas dissolution, edited by L. N. Z. Limited.
Higbie, R. 1935 The rate of absorption of a pure gas into a still liquid during short periods of exposure. Transactions of the American Institute of Chemical Engineers. 31, 365.
Calderbank, P. H. & Moo-Young, M. B. 1961 The continuous phase heat and mass transfer properties of dispersion. Chem. Engng Sci. 16, 39-54.
Clift, A., Grace, J. R. & Weber, M. E. 1978 Bubbles, Drops, and Particles. Academic Press, Inc. New York.
Akita, K. & Yoshida, F. 1973 Gas Holdup and Volumetric Mass Transfer Coefficient in Bubble Columns Ind. Eng. Chem. Process Des. Dev.12 (1), pp 76–80.
Liao, Y. & Lucas, D. 2010 A literature review on mechanisms and models for the coalescence process of fluid particles. Chemical Engineering Science. 65(10), pp 2851–2864.
