(122a) Tray Operating Window - Description and Applications

Stable and effective operation of distillation trays are characterized by vapor and liquid loads falling within a number of limitations imposed by the tray geometry. Flooding, limits capacity of trays and can be induced by vapor and/ or liquid rates. At the low operating end, weeping, dumping and/ or flow regime transitions can severely affect the ability of a tray in achieving the desired separation. Significant amount of research has been done over the years for correlating those limitations to operating conditions, physical properties of fluids involved and tray geometry. Tray designers rely strongly on those correlations for optimizing the design of a tray based on a given set of process loads and physical constraints. Those correlations can be used to plot tray operating limits as a function of liquid and vapor loads for a given tray geometry and are often referred to as tray operating windows or stability diagrams. Those diagram are extremely useful to process engineer in setting up operating conditions or making process adjustments that ensure effective fractionation in tray towers. They are also a valuable tool for a trouble shooter when assessing poor performance of distillation towers. This paper describes the different limits plotted on typical tray operating windows and their applications in process design and operation through a few practical examples.