Drawoff liquid

The minimum liquid head above the drawoff nozzle must be greater than the nozzle exit resistance. Based on a safety factor of 4 and a velocity head K factor of 0.5 ... 

For a saturated (bubble point) liquid, pipe vertically downward from the drawoff nozzle as close to the nozzle as possible. This gives maximum static head above any horizontal sections or piping networks ahead of the pump. 

When a small quantity of a second liquid phase is present, a drawoff pot (commonly called a bootleg) is provided to make separation of the heavy liquid (frequently water) easier. The pot diameter is ordinarily determined for heavy phase velocities of 0.5ft/min. Minimum length is 3 ft for level controller connections. Minimum pot diameter for a 4 to 8 foot diameter reflux drum is 16 inches. For... 

Here, we refer to small amounts of water rather than large slugs that could damage the trays. Often the water will boil overhead and be drawn off in the overhead accumulator bootleg (water drawoff pot). However, if the column top temperature is too low, the water is prevented from coming overhead. This plus too hot a bottom temperature for water to remain a liquid will trap and accumulate water within the column. The water can often make the tower appear to be in flood. 

Xy, = composition of liquid in still, mol fraction Xj = mol fraction of component in liquid phase X = mol fraction of more volatile component in liquid xjj = instantaneous mol fiaction of the component in the distillate that is leaving the condenser at time 0. X]3i = initial distillate composition, mol fiaction xj = mol fraction component in liquid phase y, = mol fiaction of component in the vapor phase D = mols of distillate per imit time, or mols of distillate at time 0, or distillate drawoff. 

Pj = pure component vapor pressure, mm Hg R = reflux ratio (liquid returned to column)/(distillate drawoff) subscripts indicate number of plates, Rjnin... 

Multiple feeds, both liquid and vapor, and sidestream drawoffs, both liquid and vapor, are permitted. A general nth tray is sketehed in Fig. 3.13. Nomenela-ture is summarized in Table 3.1. The equations deseribing this tray are ... 

Complex towers. Interreboilers, intercondensers, cooling coils, and side drawoffs are more easily incorporated in trays than in packed towers. In packed towers, every complexity requires additional distribution and/or liquid collection equipment. 

Liquid collectors are installed when liquid must be collected for redistribution or drawoff (e.g., for external cooling). The common device used is a chimney tray, which is similar to an orifice redistributor, but without perforations. Another common device is the Chevron-type collector, which is a series of Chevron blades, with liquid being collected at the bottom of the blades. 

Intermediate liquid outlets. Liquid may be withdrawn using a chimney tray or from a downcomer. A chimney tray is a flat, unperforated plate with vapor risers. It permits total withdrawal of liquid a downcomer drawoff permits only partial withdrawal because some weeping occurs through the tray. A downcomer drawoff may contain some entrained gas, which must be separated downstream or allowed for in downstream equipment design. 

Liquid sidestreams are used when there is less A in the feed than B or C. The vapor passing up through the sidestream drawoff tray contains all the A that is in the feed. The concentration of A in the liquid phase on this tray is smaller than its concentration in the vapor phase since A is the most volatile component. Therefore we withdraw a liquid sidestream. In the case where there is less C in the feed than A or B, we use a vapor sidestream below the feed. The concentration of the sidestream impurity C is less in the vapor phase than in the liquid phase since C is the heaviest component. 

Sidestream column with stripper. Higher-purity sidestream products can be obtained if a stripping column is used in conjunction with a sidestream column. The liquid drawoff stream from the main column is fed onto the top tray of a stripper. The stripper has a reboiler, which produces vapor to strip out most of the light component A. 

I I Backflow is most simply defined as a reversal of the normal direction of flow of piped liquids. It happens when, for one reason or another, upstream pressure falls below downstream pressure. Backflow can result from a pump failure, heavy upstream drawoff, downstream pressure rise, ruptured lines and many other conditions. 

Sample drawoff connections, usually for liquid from the trays, but some top (overhead) and reboiler vapor as well as liquid can be very useftil. 

Problem A horizontal liquid/liquid separator experienced siphoning in a drawoff loop seal in the heavy phase bottom drawoff line. This produced erratic flow and level so the siphoning needed to be stopped. A 50 ft drop from the top of the loop seal to grade produced a strong suction. 

In these equations, CfJ and Cfj are the concentrations of component i at the outlet and the inlet of column /, respectively. Qj is the actual volumetric flow rate of mobile phase through column j. It is related to the liquid phase velocity, Uj, by Qj = eAuj, where A is the column cross-section area, which is assumed, without loss of generality, to be the same for all the columns including the feed and drawoff columns. 

Centrifugal separation of immiscible liquids (a) bowl at rest (b) bowl rotating. Zone A, separation of light liquid from heavy zone B, separation of heavy liquid from light. (1) Heavy-liquid drawoff. (2) Light-liquid drawoff. 

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