Extending the Operating Range of Cross-Flow Trays

The capacity of a cross-flow tray is limited by gravity. When the vapor velocity exceeds the terminal velocity of the droplets, the droplets are carried to the tray above. This leads to a reduction in tray efficiency and could be seen as one of the capacity limits of the tray. When trays are operated in the spray regime (low liquid rates) droplet entrainment is one of the main factors limiting the tray capacity. In general cross-flow tray efficiency values are poor for trays operating in the spray regime. Centrifugal motion can be used to overcome the limitations imposed by gravity. Koch-Glitsch developed a new tray that uses centrifugal contacting devices instead of the valves typically seen on conventional cross-flow trays. These centrifugal devices can handle higher vapor rates before spray entrainment limits the capacity. By arranging the centrifugal contacting devices the same way as valves on a conventional tray, the efficiency enhancement of liquid cross-flow can be harnessed. This new tray arrangement was tested in a 5.5 ft diameter distillation tower. Capacity and efficiency information were generated. The data from these tests will be presented and the range of applicability of this new tray will be discussed.