High capacity trays have been the revamping success of the 90's. The decade started with only one major choice for high capacity tray operation, the UOP MD(tm). Now every medium and larger sized equipment vendor has its own proprietary high-capacity tray. Some vendors offer multiple types. They have added low-cost revamping opportunities for many services not suitable for structured packing. However, relatively few high-capacity trays are in service compared to structured packing or more traditional trays. With every new advance a learning curve of painful experience follows. Basic concepts in high-capacity trays are presented. The objective is to give the engineer the tools to sort out what is possible, what may be possible, and what is hype.
The most common steps to high-capacity use (1) increased active
area by using hanging downcomers, (2) using smaller valves or
sieve holes, (3) directional valves, and (4) eliminating downcomers
entirely. Each combination of options has specific affects on
liquid capacity, vapor capacity, flexibility, and cost. Every
application has a choice of specific options that fit it best.
The basic advantages and limitations of each of the engineering
choices is explained. Basic recommendations on what is possible
and what is not possible are made.
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