IMPROVING FLOW PATTERNS IN A DISTILLATION TRAY BY MODIFYING DOWNCOMER APRON SHAPE

Abstract

A simple modification of the downcomer apron shape has been proposed and experimentally studied. Experiments were carried out in a 40 [cm] diameter tray with water and with no vapor flow. Weir length to diameter ratios were varied from 0.6 to 0.775 and water flow rates between 150 and 600 [cm³/s]. Curved, triangular, trapezoidal and toothed apron shapes were tested. Velocity distributions on the plate were measured using the hydrogen bubble technique up to a flow rate of 200 [cm³/s]. Stagnation point loci were determined for all operating conditions, and the fractional forward-flow area (FFA) was then calculated. The FFA's were considered a measure of the efficiency of the tray, and hence used to compare the performance of the various apron shapes.

Three flow patterns were experimentally observed: regular, inverted and transition. Flow pattern maps were obtained, which permit the selection of an optimum shape when an appropriate scale up criterion is used. To this end, it was found that the best criterion was to use the same liquid residence time in the prototype and model. The results proved that the FFA values for a modified apron were always higher than for the standard or conventional apron. This is important in tray design, since it provides an easy way of improving distillation plate efficiencies.

KEYWORDS:

• Distillation
• Flow patterns
• Trays.

Additional information

Notes on contributors

L. ANTONIO ESTÉVEZ

Author to whom correspondence should be addressed. Present Address: University of Puerto Rico, Department of Chemical Engineering, P.O. Box 5000, Mayaguez, PR 00709-5000.