Page 313 - Applied Process Design For Chemical And Petrochemical Plants Volume II
P. 313
302 Applied Process Design for Chemical and Petrochemical Plants
Note: 1 in. water/ft = 1.87 mmHg/ft = 6.15 mmHg/m
Superficial vapor velocity, V, = G/ (pd) (9-35)
where A = (x/4) D2, ft2
Packing Efficiency/Perforance for IMTP Packing [96]
This is usually expressed as HETP, and for the IMTP
packing when a high performance (uniform) liquid dis-
tributor is used in a column, the HETP is independent of
the tower diameter and packing depth. Norton [83] has
developed a concept for evaluating HETP for fluids (a)
non-aqueous, (b) non-reacting and non-ionizing, and (c)
low relative volatility (less than three) [83], as follows:
System base HETP of IMTP packing for distillation and
reboiled stripping:
[J-0.16 CS - CAPACITY FACTOR FT./SEC.
(1.78)p, For p S 0.4cp (9 -
(A) System Base HETP = A -
(B) System Base HETP = B [4-0.19 Figure 9-28. Packing comparison at design point for Intalox@ ceram-
ic saddles, metal pall rings, and metal Intalox". Reproduced by per-
-
[JLIO-~~ (9 - 37) mission of American Institute of Chemical Engineers, Strigle, R. F., Jr.
and Rukovena, F., Chemical Engineering Progress, Mar. 0 (1979) p.
for p > 0.4 cp 86; all rights reserved.
expressed as millimeters or inches, depending on con-
stants used for A and B in the previous equations. If (T > 27,
use (T = 27, dynes/cm; p = liquid viscosity, cp, Use the val-
ues of A and B as follows [Reference 83 by permission] :
Values of A and B for Equations 9-36 and 37 24,000 #/day -
IMTP Size No. 15 No. 23 No. 40 No. 50 No. 70 l l
A-mm 271.3 331.4 400.7 524.9 759.9
A-in 10.68 13.05 15.78 20.67 29.92 U
B-mm 296.7 366.1 438.3 579.9 831.2 450F 1
Bin 11.68 14.41 17.25 22.83 32.72 97,300 #/day reboil
For commercial towers with good liquid/vapor distribu- 107,400 #/day + 10,100 >
tion Norton [96] recommends standard designs use
HETP dues 13% above the system base HETP. If the sys- Figure 9-29. LHC plant stripper using packed tower; for Example 9-1.
tem under consideration does not meet the physical prop-
erties limit, either use a conservative estimate or use actu-
al plant or published data for the system. For comparison Specifications to be:
of HETP values for selected packings see Strigle and Overhead 90% ethylene
Rukovena [94], Figure 9-28. Bottoms: 95% ethane
Feed: 13,000 lb/day ethylene
Example 9-1, Hydrocarbon Stripper Design (Figure 9-29) 11,000 lb/day ethane
Determine feed temperature from ethylene tower.
Design a packed tower splitter for a light hydrocarbon Bottoms: 25"F, Boiling point feed
plant. The conditions of operation as determined from Bubble point of bottoms: At 445 psia
material balance are:
----
Operate at 430 psig, feed from ethylene tower at purifi- Composition x~ K@47"F Kx K@45"F Kx
cation unit. Ethylene 0.05 1.36 0.068 1.35 0.067
0.95
Feed: Volume: 55% ethylene Ethane 0.95 1.0 - 0.97 0.921
--
43% ethane 1 .oo 1.018 0.988
