How often do maintenance personnel open a column during a shutdown and find tray panels dislodged without any apparent damage?
How about tray valves stuck in the bottom pump suction? While the initial reaction may be to blame faulty installation for not tightening hardware properly, 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, a column that has lost its roundness; weld-ins that are out of tolerances; and the changing forces under operating conditions may cause the panels to shift position. When the shift directionally pulls the panels farther apart and reduces the overlap, the hardware can become loose, and panels can be completely 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 three-quarter inch in all overlaps to increase the tray’s reliability.
In a through-bolted design, one tray panel rests on the integral truss of the adjacent panel. Unlike the friction washer design, the bolt passes fully through both panels. 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 to significant efficiency problems on a tray. Operators have long found floating tray valves in mysterious downstream places.
While trays operating at maximum capacity can generally tolerate a few missing valves without huge efficiency losses, turndown capacity will be impacted significantly.
For trays with round-shaped floating valves, it is common to find 10-20% of valves missing during an inspection. The small, three-legged configuration, coupled with the rotation that allows the valve’s popup movement, makes round-shaped floating valves especially susceptible to detachment from the tray. The resolution requires a design 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 inherently more resistant to popping from the tray deck.
Sulzer’s replacement shop and warehouse — located in Humble, Texas — maintains a large inventory of tray hardware and replacement valves to replace those found missing during inspections. Sulzer has the capability to fulfill field service needs and quickly provide customers with replacement trays, structured packing and internals.
For more information, visit sulzer.com.
