Page 184 - Applied Process Design For Chemical And Petrochemical Plants Volume II

Distillation I 73

0.0138
132.2
hPc = 0''98 ( 30.5 - 0.0138) (x) 0.0861 hdu = 0.56 2
0.118
8. Slot pressure drop, Rectangular slots 2. Segmental, upflow when inlet
, ,2/3 weir used Neg. Neg.
1/3 I hd' = 0.3 Vdu2
h, = 32 3. Total segmental loss, hd 0.000077 0.00007'7
4. Circular downspout
5. Liquid height in downcomer
= 0.626 0.626 0.566 Hd = hw + how + hd + h, + A
d. Liquid Gradient = 2.5 + 0.0989 + 0.000077 +
Mean tray width = (4 + 6)/2 = 5 ft 1.638 + 0.35 4.58 4.36
GPM/ft mean tray width = 3.74/5 = 0.75 6. Free height in downcomer
Assumed mean liquid depth, hl = F = St + hlv - Hd = 24 +
2.5 + 0.0989 + 0.1 2.5 - 4.58 21.69 21.71
Uncorrected A'/row caps = approx. 7. Throw over weir
0.02 in. f = 0.8 [how (F)J112
V, (P,)''' = 4.67 (0.0138)1/2 = 0.548 = 0.8 [0.0989 (21.69)]'12 1.17 1.17
C&, from Figure 81 13 = estimated h. Vapor distribution ratio
0.55 (off chart) Rv = A/h, = 0.12/0.87 0.138 0.141
No. cap rows = 11 i. Slot seal
Corrected A = (0.02) (0.548) (11) Dynamic, hd, = h,, + how +
= 0.1206 inches 0.12 0.12 A/2 = 0.5 + 0.0989 + 0.06 0.65 0.65
A/2, inches (essentially negligible
in this case) 0.06 0.06 Liquid Velocity in Downcomer
e. Total pressure drop per tray, in. liquid
1. Modified Dauphine Minimum cross-section area of downcomer = 0.886 ft2
h, hc + h,, + h,, + A/2
ht = 0.87 + 0.5 + 0.0989 + 0.06 1.528 1.505 Liquid rate = 0.00834 ft3/sec
2. Bolles Velocity = 0.00834/0.886 = 0.00942 ft/sec
ht = h,, + h, + h,, +how + A/2 =
0.118 + 0.626 + 0.5 + 0.0989 + This is very low and confirms that there should be
0.06 1.502 1.310 ample disengaging capacity in the downcomers. The
f. Pressure drop for 15 trays in downcomers are too large for good design.
rectifjmg section
1. Modified Dauphine, 15 (1.528) Slot velocity
= 22.9 in. liquid = 34.2 mm
Hg 34.2 mm The results of lines R, S, and T indicate that the vapor
2. Bolles, 15 (1.502) = 22.4 inches velocity through the cap slots is lower than desirable for
liquid = 33.4 mm Hg 33.4mm good bubbling.
Pressure drop for 5 trays in
stripping section Slot Opening
1. Modified Dauphine, 5 (1.505)
= 7.52 in. liquid = 11.1 mm The slot opening, h,, given in line c8 is only slightly
2. Bolles, 5 (1.42) = 6.56 in. liquid = 9.7mm lower than the normal design of 50-6096 of H,, or 0.75 in.
Total pressure drop for 20 trays to 0.90 in.
1. Modified Dauphine 45.3 mm
2. Bolles 43.1 mm Vapor Distribution Ratio
g. Height liquid in downcomer
1. Segmental, underflow plus The values of line (h) are quite in line with good vapor
friction 0.000077 0.000077 flow through all the caps. This is as would be expected,