Page 141 - Applied Process Design For Chemical And Petrochemical Plants Volume II

130 Applied Process Design for Chemical and Petrochemical Plants

The “C” factor is determined at the top and bottom
(or intermediate) positions of the column in order to
evaluate the point of maximum required diameter. The
“W rate obtained in this solution is the maximum allow-
able, and hence corresponds to the minimum acceptable
diameter for operation with essentially no entrainment
carryover from plate to plate. Normally a factor of
“safety” or “ignorance” of 1.10 to 1.25 would be applied
(W divided by 1.10 to 1.25) if irregularities in capacity,
Standard Dimensions: system pressure or other significant variables can be
Diameter: 17b”
Initial Opening: 0.10“ anticipated. Recent experience indicates that the rela-
V-1, V-4, GV-1, and V-1 H tion is somewhat conservative for pressure (5 to 250 psig)
operated distillation systems, and the maximum allow-
Figure 8-74a.
able rate can be increased by 5-15% (W times 1.05 to
1.15) exercising judgment and caution. Basically this
reflects the satisfactory operation at conditions tolerat-
ing some entrainment with no noticeable loss in frac-
tionating efficiency. In any case the shell diameter
should be rounded to the nearest inches on the diameter
for fabrication standardization. Diameters such as 3 ft,
8% in. inside diameter are to be avoided, but can be used
if conditions warrant. Standard tray layouts for caps,
Standard Dimensions: weirs, etc. are usually set at 6-in. intervals of diameter
Diameter: 17N starting about 24 to 30 in.
Initial Opening: none (flush seating)
The diameter based on vapor flowrate, V‘, in the region
V-lX, V-4X, GV-lX, and V-1 HX of greatest flow:
Figure 8-74b.
1/2
D=[:($)] (8 - 220)

Entrainment may not be the controlling factor in
proper design. In cases of high liquid load or with
extremely foamy or frothy fluids the tendency to flood
V-1 TYPE is generally increased by close tray spacing. The
(Fiat Orifice) hydraulics of the tray operation must be evaluated and
Figure 8-74c. the liquid height in the downcomer reviewed for
approach to flooding. If liquid height in the downcomer
exceeds one-half the tray spacing, the spacing should be
Diameter of Orifice Opening: 1 17/32“
increased and the column rechecked. In such cases
entrainment is of no worry as the allowable entrainment
vapor capacity will be greater than needed to satisfy the
increased tray spacing.

Tray Layouts

Flow Paths

(Extruded Orifice) The simplest tray arrangement considering fluid flow
Figure 8-74d. and mechanical details is the cross-flow shown in Figure
8-84 (page 137). It fits the majority of designs. When liq-
Figures 8-74a-d. Glitsch Ballast@ Valves, V-series. Used by permis- uid flows become small with respect to vapor flows the
sion, Glitsch, Inc., Bul. BU-69 (Rev.).