Cross-flow-trays belong to the important internals of distillation columns. Since the last years different manufactures implement high capacity trays. Aim of these trays is to increase the working range by constructive modifications. To reach higher capacities columns are often revamped with these new trays. Actions to increase the capacity of a tray are:

• Use of truncated downcomers to increase the active area of the tray,

• Use of demisters above the trays to reduce liquid entrainment to the next tray,

• Use of new valve geometries, e.g. new fixed valves, or new tray geometries, e.g. trays with a wave-like surface, to increase the efficiency of the trays.

For many of these new features neither experimental investigations nor calculation models are available. This makes it difficult to assess high efficiency trays.

The hydraulics of elements of high capacity trays was investigated experimentally in an air-water-simulator (diameter 500 mm). The experiments included the investigations of new types of valves, the influence of droplet demisters above the trays, the efficiency of wave-like trays and the specialty of truncated downcomers. The investigations show some surprising results and can help to understand the function of high capacity trays.