Page 348 - Applied Process Design For Chemical And Petrochemical Plants Volume II

Packed Towers 337

Pressure Drop, in H20/ft
0.7 I
0.6 Grid A
0.5 where V, = vapor rate, ft?/sec
0.4 Grid B VL = liquid rate, U.S. gpm
0.3 A = tower area (JG 9)
f?*
0.2 h, = vapor density, lbs/ft3
0.1 p~ = liquid density, Ibs/ft3
oj I
0.1 0.2 0.3 0.4 0.5 Typical pressure drops are shown in Figure 9-60. Mass
Vapor Rate, Cs, fils transfer and heat transfer evaluations should be referred
Figure 9-58. Nutter Snap-GridTM typical performance charts for pres- to the manufacturer.
sure drop. Used by permission of Nutter Engineering, Harsco Corp.,
Bull. CSG-2, for Air-lsopar Q 1 OgpWft2. Glitsch-GridTM [lo71 (Figure P6UU)
This is an open area packing with multiple layers of lat-
tice-type panels. This grid, as described by the manufac-
turer’s bulletin, consists of vertical, slanted, and horizon-
tal planes of metal. The vertical strips have horizontal
flanges oriented alternately right and left. Due to the ran-
dom overlap, the vapor path must zig-zag through the bed.
Per the manufacturer, this grid has extremely low pres-
sure drop (0.5 mm Hg/ft) at capacities higher than is pos-
sible with any other mass transfer device. Grid capacity is
approximately 50% greater than conventional trays, and
about 35% greater than 3?4in. ballast rings. The grid is
highly resistant to fouling, plugging, or coking by tars or
solids. See Figures 9-61A and 961B for pressure drop and
capacity performance comparison. HETP is available from
the manufkcturer and final design performance must be
obtained from the same source.
Structured Packing Technical Performance Features

Fair and Bravo 11081 have performed extensive studies
on structured packing and have developed general mod-
els for flooding, pressure drop, and mass transfer. Struc-
tured packing is now generally considered cost effective
for moderate pressure and vacuum distillations when
compared to trays and random packings [108]. The test
work of the authors considered the trade-named struc-
”
0 10 20 30 40 50 60 70 tured packings of Intalox@, Gempa@, Flexipac@, Mella-
Liquid Rate, Ct pak@, Sulzer, and Montz in their studies. See earlier fig-
ures for installations of these packings, many of which are
quite similar. All of the cited packings are corrugated
Figure 9-59. Comparison of capacities of Flexigrid@ Styles 2 and 3 sheet type designs, except the Sulzer, which is a fabricat-
at flooding with 2-in. Flexiring” random packing, and a competitive ed wire gauze construction. Table 9-38 summarizes the
grid. Used by permission of Koch Engineering Co., Inc., Bull. KFG-2.
characteristics of the selected packings. Refer to the
respective manufacturers for confirming details and
design application techniques.
>
-4 “viscosity correction” should be made if p~, 10.0 cp
by multiplying the “% flood” obtained from Equations Hmding
in
cp.
9-72 through 973A by the term “p~,-~~”
At flooding or near flooding conditions [ 1081 :
1. A rapidly increasing pressure drop with a relatively
slight increase in gas rate (hydraulic flood) develops.