1987 Volume 13 Issue 5 Pages 533-541
To design a compact upper column for a liquid air distillation system reasonably, and to determine the optimum, location of side-cut stage for improving argon yield, it is necessary know clearly the point efficiency at high load.
In this work, a small-scale distillation test apparatus was manufactured which had a 0.1-m column diameter and four stages of perforated plates. Many design factors were tested such as outlet weir height and open free area as plate geometry, and N2-O2 and Ar-O2 systems at high load, under upper column pressure and total reflux as operation conditions.
Vapor-phase oxygen concentration was measured at each stage, and Murphree vapor-phase plate efficiencies were calculated on the basis of the definition.
Based on the fact that the liquid flow path length is very short on the stage, and load is very high, it can be assumed that liquid flow is perfectly mixed with vapor flow on the tray, so that plate efficiency is equal to point efficiency.
Estimation accuracy was improved by correcting conventional works. The double film theory was assumed for point efficiency of the liquid air distillation system. Open free area was related to experimental constant in NG and expression of liquid holdup on the tray. Results from study of pressure drop in liquid air system were applied as the liquid holdup, which was necessary for estimation of contact time of vapor liquid mixing on the tray. The estimation method of point efficiency by using these factors was proposed.
Its accuracy is estimated as within 1.8% of concentration difference for the N2-O2 system, and within 2.5% the for Ar-O2 system.
