Page 333 - Applied Process Design For Chemical And Petrochemical Plants Volume II

322 Applied Process Design for Chemical and Petrochemical Plants

Second Assumption: Try 15-inch Dia. Ceramic Tower From Figure 9-46D, correction for viscosity = 1.1 (at 18 cp)
h,, for acid = how (0.6) (1.0) (1.1) = (0.0384) (0.66)
Inspection of Figures 9-21B, C or D shows that the = 0.0234 ft3 acid/ft tower volume
increase on tower diameter is not reflected in the value of
the abscissa. By changing the tower diameter to 15-in. For a packed volume of 15 ft in a 15-in. I.D. tower, the
cross-section area = 1.22 ft*. total acid hold-up:

G=-- 0”725 - 0.593 lb/(sec) (ft2) = [(15) (1.22)] (0.0254) (112.6 lb/ft3)
1.22
Total hold-up = 52.3 lb acid
L = 0.461/1.22 = 0.378 lb/(sec) (ft2)
Whghts
Weight of dry packing in tower:
a
G~ i ) v2 po.2
- (0.1535)
=
PC E3 PL gc = (42 lb/ft3) [(15) (1.22)]
This indicates operation in the loading region. The = 770 lb
expected pressure drop is 0.5 in. water/ft. Total weight on bottom support plate when operating
Total expected pressure drop:
(not flooded)
Packing = (0.5) (15) = 7.5 in. water
Support = 1.5 in. (estimated from Figures 9-37 and -38, -39, and = 52.3 + 770 = 822.3 lb
40 for a 58% open grid).
Total drop = 9.0 in. water (approximate) Some allowance should be made for surging or uneven
operation.
Superficial gas velocity through tower: The maximum expected weight of liquid would be at
flooding conditions:
0.593 lb/(sec) (ft2)
3
0.087 lb/ft3 Using percent free gas space = 77.5
Volume of liquid space = (15) (1.22) (0.775)
= 14.2 ft3
Entrainment
Weight of acid in this space = (14.2) (112.6)
This velocity is slightly high and an entrainment knock- = 1,600 lb
out or separator should be installed in the air stream fol- Maximum support load = 770 + 1,600 = 2,370 lb
lowing the tower, or in the top of the tower itself.
This is the load that should be considered for the sup
Liquid Holdap in the Tower: port design and selection. To allow for unusual conditions,
specify support load = (1.1) (2,370) = 2,60@1b minimum.
For water, the hold-up would be, from Equation 9-54.
Structured Packing

Structured packings as in use at the present time are
composed of:
d, = 0.68 (from Table 9-7)
1. Wire-mesh weavings (Figures 9-W, 9-6Z, 9-6AA-FF) .
[ (0.378) (3600)f’6 c 0.0384ft3/cu ft
h, = 0.0004 2. Corrugated sheet, or crimped sheet (usually some-
(0.68) for water. what thin) (Figures 9-6GG-NN) .
3. Grid-type, open, heavy (usually metal) bar-grid
For sulfuric acid: shapes stacked together (Figures 9-6 00-TT) .

From Figure 946C, h,/h,, for density correction multipli-
er = 0.6. Structured packings vary as to the preferred process
From Figure 9-46B, correction for surface tension = 1.0 (at application depending on the geometric arrangement of
70 dynes/cm) the components and: