Page 185 - Applied Process Design For Chemical And Petrochemical Plants Volume II

1 74 Applied Process Design for Chemical and Petrochemical Plants

since the hydraulic gradient is low; too low to require any Conclusion
compensation.
This is not a good tray design, but it should operate.
Liquid Entrainment However, a reduced efficiency is to be expected due to low
vapor velocities.
vf= 132.2/[28.28 - 2(2.12)] = 5.5 ft/sec Because the liquid flow is low also, %in. v-notched weirs
should be used to ensure uniform flow and level across the
I/ 2
tray. The bottom of the notches should be 2.5 in. above
the tray floor.
St
1/ 2 Sieve Trays with Downcomers
27.3
+
= - 10.75 (5.5)
24 ( 5O.:!!;l38)
The performance analysis of these trays is quite similar
= 1.13 + 0.978 = 2.108 to bubble caps, but more so to valve trays, because the tray
has the same basic mechanical features. The difference
Reading Figure 8-1 16 being that bubble caps and valves are replaced by perfo-
For 27 dynes/cm surface tension rations or holes in the tray for entrance of the gas to the
liquid on the tray. Figures 8-67A and 8-118 and 119 repre-
W,/h, + h,, + h, = 0.026 sent the general construction of a sieve tray.
Sieve trays have been used in both clean and fouling ser-
We = (.026) (0.098 + 0.5 + 0.626) = 0.0317 lbs/min ft2)
vice, including solutions of suspended particles. The bub
Entrainment = (0.0317) [28.28 - 2(2.12)] = 0.764 lbs/min bling action seems to wash the solids down from tray to
tray provided there are no corners or “dead” spots on the
Entrainment ratio = 0.764/ (6565/60) = .00698 tray. Sieve trays are preferably selected for applications
which can be operated at from 5&100% of capacity with-
This value of entrainment is negligible. For a new col- out too sudden a surge from one rate to another signifi-
umn design, this would indicate that the tower was too cantly different. When operating within the design range,
large, and a smaller shell should be considered. the efficiency of these trays for many systems is better than

Top Removable Manwoy
Typical Ring Support Varied Beam Designs-
Shop or Field Welded Fabricated to Meet
to Tower Wall. Specific Job Demands.

Large Diameter Troy Top and Bottom
Supported by Major Removable Manray.
Beom.

Perforated to Meet Downcomer-
Individual Requirements Affixed to a
Downcomer Bor

Perforated Shower Weir - Fixed or
Troy Adjustable, per
Specificotions
[or as Required).

Special Supporting Ring Disc or Accummulator
Trays-and Trops,Seal
Pans and Draw Off
Bones Fabricated to
Your own Design Figure 8-118. Sieve tray with downcorners, tower
Specificotions. assembly. Used by permission, Hendrick Mfg. Co.