Page 104 - Applied Process Design For Chemical And Petrochemical Plants Volume II

Distillation 93

Typical calculations: starting at bottom and working up
~
(Xi/xh)l (%)3 (xi/Kh)4 (9)4 (%/xh)5 (%)5
.- ~ the column.
A 325.24 0,9952 200.81 0.9916 126.61 0.9851
B 1.0 0.00306 1.0 0.004938 1.0 0.007781 Tray 1: Component A
C 0.514 0.001573 0.682 0.00337 0.908 0.007065
326.754 202.492 128.518
.- .~
(xi/xh)6 (xi16 (xi/xh)7 (%I7 (xi/Xh)ll (%I8
-. ~
A 80.60 0.9736 52.05 0.9520 33.97 0.9138 (3.84) (0.0249) + 0.010
B 1.0 0.01208 1.0 0.01829 1.0 0.0269 = 1.905 I
1.633
C 1.213 0.01465 - 2.21 0.05945 3.84 (0.1382) + 0.101
0.02987
82.813 54.683 37.18
.- -. , -. .- - ~
(Xj/Kh)9 (%)9 (xi/xh)lO (%)lo (%/%)I1 (xi111
A 22.47 0.8491 15.196 0.7501 7.716 0.5421
B 1.0 0.03779 1.0 0.04936 1.0 0.07026 Tray 2: Component A
5.516
C 2.994 0.1131 - 0.2005 __ 0.3876
4.061
_- 26.464 -- 20.257 14.232 (K/Yh)Z = 1.905 (3.84) (0.0543) + 0.010 1
_- -
- - -
Ratio of keys in feed = 0.456/0.0555 = 8.2 3.84 (0.170) + 0.101
Ratio of keys on Tray No. 10 = 0.7501/0.04936 = 15.2 = 0.552
Ratio of keys on Tray No. 11 = 0.5421/0.07026 = 7.7
Continuation of the calculations gives an approximate
Tray No. 11 should be used as feed tray (counting down match of ratio of keys in feed to those on plate 10. Then
from the top). Note that since the relative volatility did not feed tray is number 10 from bottom and this is also num-
change much from top to feed, the same value was satis- ber 11 from top.
factory for the range. Liquid mol fraction ratio from vapor mol fraction ratio:

Stripping Section
Determine V,: per mol of feed
1 1 Ratio on tray no. 9 = 15.018/1.905 = (xi/xh) = 7.9
(L/V), = ~ = - 0.75
=
1+D/L l+L Ratio on tray no. 10 = 19.16/1.905 = 10.05
3 Ratio in feed = 8.2
Total theoretical trays = 11 + 10-1 (common feed tray count)
vr=-= (L/D)D 3 (0.45145) = 1.806 = 20 not including reboiler
(L/T.’) 0.75 Total theoretical stages = 20 + 1 (reboiler) = 21

L, = (L/D) (D) = 3(0.45145) = 1.35 mols/mol feed This compares with 19 theoretical stages from Gilliland
Plot.
L, = L, + qF = 1.35 + 1.298 (1.0) = 2.648
Tray Efficiency
Vs = Vr - F( 1 - 9) = 1.806 - (1.0) (1 - 1.298) = 2.104
Use average column temperature of 271°F and feed
Vs/B = 2.104/0.54804 = 3.84
analysis.
Relative volatilities, ai, determined at average tempera- .~
F9 cp
ture between bottom and feed of column. Usually the Component . - . .u XiF . -- VP- adh
-
.-
pinch temperature gives just as satisfactory results. A 0.456 0.28 0.128 2500 1.94
. - B 0.0555 0.36 0.020 1290
.
component %B YiB (%)avg (yi/yh)l @i)l 0Ti/yh)2 @i)2 C 0.362 0.37 0.134
D 0.0625 0.40 0.025
A 0.010 0.0249 1.905 0.319 0.0543 0.552 0.107 E 0.0625 0.48 o.030
B 0.101 0.1382 1.00 1.000 0.170 1.00 0.194
C 0.660 0.6700 0.740 3.800 0.647 3.08 0.597 P = 0.337 CP
D 0.114 0.1012 0.648 0.517 0.088 0.389 0.0754 a Z (p) (x~F) = 1.94 (0.337) = 0.654
E 0.114 0.0664 0.411 0.0411 0.1476 0.0286
5.877 5.1686 Using Figure 8-29
-