Important tray design features that improve column operating reliability

How often does Maintenance personnel open a column during a shutdown and find tray panels fallen without any obvious damage? How about tray valves stuck in the bottoms pump suction? While the initial reaction may be to blame faulty installation where the hardware was not properly tightened, the answer often lies in the design of the tray. Reliable column designs need to produce on-spec products at the design capacity, while operating with energy usage at a minimum. For this to be possible over an operating cycle, the tray design needs to be robust. Sulzer’s standard designs incorporate several key features to maintain reliable operation.

Preventing Dislodged Tray Panels
In a friction washer design, one tray panel rests on the integral truss of the adjacent panel. That overlapping panel is held in place by a washer, which is bolted to the adjacent panel. Note that the bolt passes through only the panel with the integral truss.

For the friction washer style, column out-of-roundness, weld-ins out of tolerances, and the changing forces under operating conditions may cause the panels to shift position. When the shift directionally pulls the panels further apart and reduces the overlap, the hardware can become loose and panels can be completing dislodged. The probability of the panel dislodging is directly proportional to the overlap dimension. Whereas some tray manufacturers keep this overlap to a minimum to reduce costs, Sulzer recommends a minimum ¾” in all overlaps to increase the trays reliability.

In a through-bolted design, one tray panel rests on the integral truss of the adjacent panel. Contrary to the friction washer design, the bolt passes fully through both panels in a through-bolted design.

For the through-bolted style, the panels are less impacted by tray vibrations or other general upset conditions. Because of this inherently higher reliability, the through-bolted connection is preferred for heavy duty applications.

Keeping Floating Valves in Place
While it is easy to see how dislodged tray panels cause lost efficiency, missing floating valves can also contribute significant efficiency problems on a tray. Operators have long found floating tray valves in mysterious downstream places. With so many valves on a tray, are these tolerable losses?

While trays operating at maximum capacity can generally tolerate a few missing valves without huge efficiency losses, turndown capacity will be impacted significantly. On top of this, replacing valves simply costs valuable manhours during a turndown.

For trays with round-shaped floating valves, it is not uncommon to find 10-20% of valves missing during an inspection. The small three-legged configuration, coupled with the rotation which allows the valve pop-up movement, makes round-shaped floating valves especially susceptible to detach from the tray. The resolution requires a design change: either adding anti-rotation tabs to the round valve tray deck or replacing the round valve with a different style valve. Rectangular floating valves, like Sulzer’s BDHTM , or fixed valve trays, like Sulzer’s MVGTM are both inherently more resistant to popping from the tray deck.

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