(172a) Non-Ideal Two-Phase Flow on Large Diameter Trays: The Stagnant Regions Model versus FRI Experiment

Forty six years ago, the Stagnant Regions Model (SRM) was published by Porter, Lockett and Lim in which the impact of severe flow maldistributions on tray efficiency for large diameter trays was investigated. The SRM involves two zones to characterize the liquid flow pattern on a single-pass tray: an active liquid channeling zone between the downcomers and retrograde/stagnant zones at the sides of the tray. It was found that for large diameter sieve trays, a loss in tray efficiency was reported due to liquid channeling and associated stagnant zones. The SRM theory was supported experimentally years later in the Aston University 1.22 and 2.44 m air-water simulator columns (Porter et. al., 1987, 1992 and 1995). At the same time the SRM was published, FRI studies on maldistributed liquid flows on 1-pass sieve trays using hydrocarbon systems in the 2.44 m FRI Low Pressure column showed no loss in tray efficiency both with and without flow control mechanisms (Bell, 1972; Yanagi and Scott, 1973).

The purpose of this paper is to discuss tray geometry parameters employed in the SRM to explain why the model predicted no loss in tray efficiency on the FRI 2.44 m diameter 1-pass sieve tray. One important parameter to be investigated is Width-of-the-Mixing-Zone (WMZ) at the sides of the tray. Arguments will be supported with FRI film footage of liquid distribution both without and with flow control mechanisms.