The influence of gas physical properties on entrainment inside a sieve tray column

Existing entrainment prediction correlations, often used in the design of sieve tray distillation columns, have been developed mostly with air/water data. Therefore, the aim of this work was to investigate the influence of gas physical properties on entrainment, by also utilising gases with physical properties notably different from air. Air, CO2 and SF6 were passed through a rectangular sieve tray column (tray hole diameter of 6.3 mm and fractional hole area of 0.156). These three gases were chosen in order to cover a large gas density range of 1.2-5.8 kg/m(3). Water, ethylene glycol and n-butanol were used as liquids in order to achieve the desired wide range of liquid physical properties. Tray spacing and weir height were set at 615 mm and 51 mm, while the liquid rate was varied from 2.9 to 80 m(3)/(hm) to cover both the spray and froth regimes. Gas flow factors ranged between 1.9 and 4.8 m/s (kg/m(3))(0.5). A database of over 500 experimental data points was generated in this study. The main objective was to use the experimental data to describe the effect of gas physical properties and gas-and-liquid flow rates on entrainment. The data were also used to evaluate the scope and limitations of current entrainment prediction models. Existing correlations fitted the air/water data well, but showed rather large deviation from the non-air/water data. A new approach to describe the influence of gas physical properties on entrainment is proposed. This approach utilises a variation of the Reynolds and Froude numbers along with the ratio of the gas to liquid density to correlate entrainment. (C) 2015 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.