Missing trays

No or low Delta P in a tower section may indicate missing trays or absence of liquid. High Delta P in a tower section may indicate that the drawoff is partially restricted or blocked, that may be due to high liquid rates in that section of the tower, flooding, or too much stripping steam. 

The contacting devices of (1) above may actually be missing, i.e., blown off one or more trays, so all that is existing is a rain-deck tray with no liquid-vapor contacting. 

Note that a restriction to vapor or liquid flow on one tray will cause the tower to flood above that tray. If, as is often done, only the trays conveniently located at manways are inspected, a plugged tray can be missed. The process engineer should not be adverse to crawling through a tower to make a thorough personal inspection. 

Starting with the feed-tray liquid as computed from the enriching section, which shows no heavy components, the mole fractions are all reduced proportionately so that their sum, plus the mole frafctions of the missing components (as shown in the feed-tray composition as computed from the exhausting section) is unity. The bubble point is then recalculated. The justification for this... 

The concentrations of the missing heavy components on trays above the feed tray are next estimated. For these, p should be very small, and Eq. (9.177) shows... 

Missing light components are added to trays below the feed in much the same manner. Thus, Eq. (9.178) for these provides... 

When the new trays were delivered, the debutanizer was taken offline, steamed out, and opened. When I entered the tower, I discovered that each and every tray in the column was totally and completely intact and clean. Everything was just as 1 had last seen it six months ago. Actually, the only thing that had changed was me. 1 had become smarter in the last six months. For example, 1 now noticed that the sides of the draw pan (see Fig. 49.3) were missing. True, they had been missing last year too, but I had not noticed their absence then. 

A standard tray set up is important so nothing will be missed (Figure 6.1). Well-marked containers are used for the four peel solutions. Folded 3" x 3" cotton gauze is used to scrub in the chemical solutions. Five or six mL of each solution is poured onto the gauze which is rung out... 

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