Stability of sieve trays with high overflow weirs

Abstract

Sieve tray columns for gas—liquid reactions sometimes operate at liquid depths much greater than in conventional distillation columns. The design of such columns requires knowledge of the conditions for stable, uniform gas distribution. Data are presented from a single 1·8 m diameter tray, operated with water and air. Pressures and weeping rates were measured as functions of air rate, liquid depth, and free hole area. The existence of a critical tray pressure drop was demonstrated, below which the gas distribution was nonuniform and high weeping rates were observed. This critical pressure drop did not depend much on the liquid depth. A 0·6 × 1·2 m rectangular tank was used to determine pressure distributions on a sieve tray under conditions of non-uniform aeration, for liquid depths up to 1·5 m. Observations on velocities and flow patterns of the gas induced liquid circulation were related to the pressure distributions. The relationship between the observed conditions for uniform aeration and the experimental pressure distribution data was investigated. An approximate theoretical concept was developed to explain and predict the limits of stability for sieve trays with high overflow weirs. Under some conditions, abnormal flow patterns can occur on sieve trays, such as oscillation and rotation of the liquid. Descriptions and explanations are given for these phenomena.