A Visual Assessment of Distillation Tray Valve Performance

When it comes to distillation column performance, tray valve design can have a dramatic impact on separation performance by affecting vapor–liquid contacting, mass transfer efficiency, operating window and column capacity. At the eChemExpo event, held April 8-9, in Kingsport, Tennessee, Elifsu Gencer, technical sales engineer, Koch-Glitsch LP used a combination of visual tools to demonstrate the relative performance of different tray valve designs.

“When it comes to column internals, their key operational objective is achieving mass transfer,” Gencer said. “And that's exactly what it sounds like: the transfer of molecules from one phase into another.”

This can happen on random or structured packing, or on trays peppered with valves that facilitate the upward flow of vapor through liquid that ideally flows across a given tray before flowing over an outlet weir into a downcomer, then across the next tray below. Liquid that leaks through the tray valves is said to be weeping, while droplets that pass through the valves in the tray above are entrained. Both phenomena negatively affect the overall separation performance of the tower.

A Picture Worth a Thousand Words

“Today we’re going to focus on the performance of tray valve designs using both traditional capacity graphs as well as visual tools such as computational fluid dynamic (CFD) simulations and plexiglass pilot-plant videos,” Gencer continued. “We’ll review historical and current valve technologies ranging from sieve trays and bubble caps to Provalves, fixed and floating Flexipros and Flexitray valves—highlighting their hydrodynamics, turndown capabilities and tendencies to weep and entrain.”

Gencer then turned to CFD to help session attendees visualize vapor jetting, spreading and deck velocity profiles, enabling optimization of valve geometry (shape, size, net rise) and directionality to improve froth uniformity and reduce maldistribution, entrainment and weeping.

Then, pilot-plant air–water tests pitted T‑valves against Flexipro floating valves, showing that the Flexipro’s downturned edges, upward extrusion and directional shape yield more uniform froth, over 30% higher capacity before entrainment, delayed weeping and provided significantly wider turndown (up to about 9:1 and even 11–12:1 in some applications) than conventional designs.

Finally, case studies on high‑pressure contactors and low‑liquid TEG (triethylene glycol) contactors demonstrated that these capacity gains can translate into smaller column diameters and substantial shell weight reductions (around 20–33%), providing both performance and capital cost benefits.

Fortunately, you need not take this journalist’s word for it when it comes to the relative performance of these various valve tray technologies. To see and hear Gencer’s case in living color, simply click on the link (no registration required) to see a video rendering of her presentation: Tray Valve Features: A Visual Evaluation