Page 328 - Applied Process Design For Chemical And Petrochemical Plants Volume II

Packed Towers 31 7

weight of packing will be approximately 50% greater than
if the same 2-in. rings had been dumped in place. Two-
inch rings are not usually stacked. In this small tower
made up of 3-ft ceramic sections, the stacking is not too
Rings
difficult a job if there are conditions which justify the extra
effort and expense.
I .o 5 IO 50 100

L'/G I Liquid Hold-up
Figure 9-43. Fraction packing wetted. Used by permission of Shul- Liquid hold up in a tower represents the liquid held in
man, H. L., Ullich, C. F., Proulx, A. Z., and Zimmerman, J. O.,A.LCb.€. the void spaces of the packing during operating conditions.
Jour., V. 1, No. 2 (1 955) p. 253; all rights resewed.
At flooding, essentially all of the voids are filled with liquid.
Usually low hold-up is desired but reasonable hold-up is
sure drop per foot will be less and the flooding point high- necessary for efficient tower operation. The weight of liq-
er than the dumped packing, it is inadvisable to go to a uid held in the packing must be considered when deter-
smaller diameter tower because of the high superficial gas mining the support loads at the bottom of the packing, as
velocity. well as the tower itself. The higher the hold-up for any par-
Using the 15-in. I.D. ceramic tower, the expected pres- ticular packing the greater will be the gas pressure drop,
sure drop will be: and the longer the tower drainage time when shut down.
Smaller size packing tends to have greater hold-up than
larger packing.
Figure 944 presents water hold-up data that are corre-
lated by [40]:
From Reference 40 for 2-in. ceramic stacked Raschig rings:

a = 0.06 (9 - 34)
p = 0.012

Liquor range checks satisfactory where h, = water hold-up, ft3 liquid/ft3 volume tower
L' = Liquid rate, lb/(hr) (ft2)
G = 0.595 lb/(sec) (f$) dp = Equivalent spherical packing diameter, inches
(diameter of packing equivalent to sphere of same
Leva [40] has shown that for liquids other than water, surface area as the packing piece). Values given for
the L must be corrected by the ratio of the density of water
to that of the fluid in the system.
L = 0.378 lb/(sec) (ft' ) (E)
0.209
=

PG = 0.087 lb/ft3

AP = 0.00258 in. water/ft packed height (estimated)

Total tower drop:

Packing = (0.00258) (25) = 0.064 in. water
(uppoximute)
Support (estimated) = 1.5 in. water
Total (approximate) = 1.56 in. water
Liquid Rate, L-lb./ft?,Hr.
Note that the weight of liquid will be greater in this Figure 9-44. Gas-liquid hold-up data for ceramic rings and saddles.
arrangement at flooding, and the operating hold-up will Used by permission of Leva, M. Tower Packings and Packed Tower
be almost the same as the dumped Intalox. The total Design, 2nd ed., U.S. Stoneware Co. (now, Norton Chemical Process
Equipment Corp.) (1 953).