Page 178 - Applied Process Design For Chemical And Petrochemical Plants Volume II

Distillation 167

-Ke, CONSTANT -C,, WET CAP PRESSURE DROP CORRECTION FACTOR
0.8 I .o

0.9
0.7
0.8
0.7
0.6
0.6
0.5 0.5

0.4
0.4
0.3
0.2
0.3
1.0 1.1 1.2 1.3 I ,4 1.5
0. I
RATIO: ANNULAR/RISER AREA
0
Figure 8-114. Bubble cap pressure drop constant (Bolles' Method).
Used by permission, Bolles, W. L., Pet. Processing, Feb. thru May
(1 956).

Figure 8-115. Correction for wet pressure drop, C,, (after Dauphine);
The pressure drop due to reversal is independent used by permission, Bolles, W. L., Pet. Processing, Feb. thru May
of slot height and riser height as long as riser height (1956), using data of Dauphine [13].
is greater than 2 in. and the cap slot height does not
exceed the riser height [ 131. When riser height is less 6. Total bubble cap pressure drop
than 2 in., the reversal pressure drop increases as long
as the slot height is less than the riser height. h, = hp, + h, (8-238)
For riser height greater than 2.5 in.:
h, from Equation 8-225 and Figure 8-106
1.71
(8 - 234)
Total Pressure Drop Through Tray
3. Dry cap pressure drop: rectangular slots. A. Bolles ' Method
The slot pressure drop through the dry cap increas-
es nearly linearly with cap diameter. (8-239)

(8 233) B. Dauphine Method
-

4. Total dry cap pressure drop
h', = hr + h, + h', (8 - 236) Downcomer Pressure Drop
5. Wet cap pressure drop
The head loss in liquid flowing down the downcomer,
(8 - 237) under its underflow edge (and up over an inlet weir, if
The correction factor, &, is obtained from Figure used) and onto the tray is important in determining the
8-115. Figure 8-115 applies to cap slots 1 in. through back up of liquid in the downcomer. There are many sug-
2 in., and if slots are smaller (around ?4 in.) the q+. gested relations representing this head loss.
factor increases about 25% average (10-50%). The
relation applies only to the pressure drop attributable A. Segmental Type Downcomer
to the conditions of liquid on the tray up to the top of
the slots. 1. Downcomer friction loss plus underflow loss