Cartridge tray

When column diameters are smaller than about 2V2 to 3 feet, a person cannot enter the column to install, inspect, and maintain the trays. Because of this limitation, a 2V2- to 3-ft trayed column is often installed, even if a smaller diameter is hydraulically sufficient. Alternatively, either packings or cartridge trays can be used, and column diameter reduced below 2V2 ft. 

The two main disadvantages of cartridge trays are leakage around the circumference and their relatively high cost. A vertical metal seal ring is often installed around each tray to minimize leakage. Success-Ail operation at liquid rates lower than 1 gpm has been claimed with a sophisticated variation of this sealing technique (308). 

Since cartridge trays are not fixed to support rings (like normal trays) they can be easily uplifted. Kitterman (2066) shows that the weight of the trays does little to resist uplift. The pressure drop sufficient to uplift a bundle is set by the shell friction, and this can be small. Uplifting has been troublesome on many occasions. In one 

Hgure 7.5 Cartridge fixed-valve (V-Grid) trays, 23-in ED assembly. (fieprinted courtesy of Nutter Engineering) 

In order to prevent uplift, adequate holddown of cartridge trays is essential. Holddown can be achieved by either fixing the top tray at a flange or by using rods fixed to the top head of the tower. 

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This is the boilup rate, which is approximately 3.3 ft vapor/sec. An approximately 1 ft 0 in. diameter column can handle this rate however, because it is in the usual size for a packed tower (or cartridge trays), the diameter must be checked using the packed tower calculations in Chapter 9 of this volume. 

Small-diameter columns. Columns with diameter less than 1 m (3 ft) are difficult to access from inside to install and maintain the trays. Cartridge trays or an oversized diameter are often used. Either option is expensive. Cartridge trays also run into problems with sealing to the tower wall and matching tower to tray hardware [Sands, Chem. Eng., p. 86 (April 2006)]. Packing is normally a cheaper and more desirable alternative. 

Placement of commercial cartridges with powdered reagents (often lyophilised or crystallised) into the flow manifold enables in-line reagent dissolution, as demonstrated by Marshall et al. [101] who designed a sequential injection analyser with a cartridge tray attached to the main selecting valve and applied it to the chemiluminometric determination of adenosine-5 -triphosphate (ATP). They described the preparation and... 

Entry into the shell of a distillation tower is made via manholes. These are usually fitted in the column so that each serves 10 to 20 trays (48, 177, 354). When the service is clean and noncorrosive, up to 30 trays or more may he served hy one manhole. When frequent cleaning is anticipated, or if the trays are large and the process of removing them through the hole is slow, the smaller number above should be used. This enables multiple crews to work on removal or installation. If the column diameter is too small to admit personnel, cartridge trays (Sec. 7.13) should be used. 

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