HYDRODYNAMICS AND GAS-LIQUID MASS-TRANSFER IN A DOWNWARD VENTURI-BUBBLE COLUMN COMBINATION

The hydrodynamics and gas-liquid mass transfer performance of a venturi, with the liquid flowing downward, were studied. Two different hydrodynamic zones appeared within the venturi. In the first zone, just below the venturi throat, the gas formed a central core and the liquid a peripheral annulus, along the wall. In the second zone, the gas core broke and formed fine and homogeneously distributed bubbles. At high gas flowrates, the first zone extended over the whole venturi, causing a sharp drop in mass transfer performance. A new two-zone model for gas-liquid mass transfer in the venturi considered that the first "annular" zone was characterized by plug flow of the liquid in the wall annulus, around the central gas core. In the second "bubbling" zone, the liquid was perfectly backmixed. The downflow venturi performed much better than the same venturi in an upflow configuration, as long as the annular zone did not occupy the whole venturi. The gas bubbles spent more time in the venturi as they were slowed down by their buoyancy. This helped increase the gas-liquid mass transfer by about 60%.