Cross-sectional area of the tower will be based on the loadings over the bottom
tray; thus
Total vapor to tray ¼ 1,251:4 mol=h
In actual cubic feet=s ¼
1,251:4 Â 378 Â 700 Â 14:7
520 Â 34 Â 3, 600
¼ 76:47 ACFS
ρ v ¼ 7:85=76:47 ¼ 0:104lb=cuft
Total liquid from the bottom tray ¼ stripout þ product þ reclaimer liq
¼ 25,748 þ 196,482 þ 2,851
¼ 225,081lb=h
lb=gal of liquid at 240
F ¼ 7:87
Gals per hour ¼ 28,600 and cubic ft=h is 3,823
ρ 1 ¼ 58:87lb=cuft:
Loading at flood ¼ K f √ ρ v  ρ 1 À ρ v
ð
Þ
f
g .
From Fig. 5 K f = 1,280 and at 60 % = 768
Then loading ¼ 768 Â 2:47
¼ 1,899lb=h sq: ft:
Let loading be 80 % flood = 1,519:
Cross À sectional area ¼
28,599
1, 519
¼ 18:8 sq:ft:
and diameter ¼ 4:9 ft call it 5 ft or 19:6 sq: ft:
Tower will contain 20 valve-type trays made up of 18 stripping trays and 2 rectifying trays. As in the case of the contactor trays, they will be spaced at 30 in. Trayed
section will therefore be 19 Â 30 in. = 570 in or 47 f. 6 in. from bottom to top tray.
The bottom of the tower (from bottom tray to bottom tangent) will be sized to
cater for a 2 min holdup of liquid to the HLL. Thus
Total liquid from bottom reboiler ¼ 196,482 þ 2,851
¼ 199,333lb=h
lb=gal at 60
F ¼ 8:35; and at 249
F ¼ 7:89 lb=gal
Then gals=h of total bottoms
¼ 199,333=7:891
¼ 25,264 gal=h
¼ 421 GPM
or 56.3 cubic ft/min
Refinery Gas Treating Processes
527