In many gasâ??liquid contactors or reactors, mass transfer from the gas phase to the liquid phase is a major player in the reactorâ??s overall production and/or economics. This talk presents chemical and hydrodynamic data from research to intensify gas-liquid mass transfer in an inverse bubble column bioreactor meant to upgrade natural gas. We measured
kLa by dynamic oxygen absorption and turbulence properties by high-speed camera particle imaging velocimetry (PIV) for four reactor heights. Physical understanding is sought by linear addition of previous theories of
kL under turbulent conditions (Calderbank & Moo-Young 1961) or bubble terminal rise conditions (Clift 1978) to determine
kLa and turbulence intensity at various locations in the reactor. We also add entrance effects according to Higbieâ??s â??penetration theoryâ? for interfacial transfer, wherein the freshly created gas-liquid interface leads to higher absorption rate than the classic Calderbank or Froessling type of equations. However, this entrance region transfer rate does not persist long enough (or cover a large enough volume fraction of the reactor) to be dominant over the mass transfer that is forced by other phenomena such as turbulence or bubble-rise-velocity. We observed
kLa values to decrease as the height of the reactor increased from 31 to 124 cm. A model was constructed in which
kL is a sum of effects from bubble terminal rise velocity, turbulence and entrance effects. As a typical bubble moves from jet region (high turbulence) to the bottom of the reactor (low turbulence), energy dissipation decreases, which leads to a decrease in
kLa value. The modeled data match experimental data well. Based upon the results we hypothesize that the best method for intensification of
kLa is by increase of a because the effect of turbulence on
kLa is muted by
a ¼ exponent. Turbulence and bubble rise velocity is found to mediate
kL in most of the reactor.
References:
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.
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.
