Geoscience Reference
In-Depth Information
Solution : Compute N OG from Equation 16.11:
YmX
YmX
mG
L
+
mG
L
1
2
m
m
m
ln
1
2
2
m
N
=
OG
mG
L
m
m
1
003
0 003
.
.
42 735
204
.
×
.
42 735
204
.
×
.
+
ln
1
=
42
735
204
×
.
1
=
458
.
Calculate the total packing height:
Z = H OG × N OG = 0.829 × 4.58 = 3.79 m
16.3.4.3 Sizing the Plate (Tray) Tower Absorber
In a plate tower absorber, the scrubbing liquid enters at the top of the tower, passes over the top plate,
and then down over each lower plate until it reaches the bottom. Absorption occurs as the gas, which
enters at the bottom, passes up through the plate and contacts the liquid. In a plate tower, absorption
occurs in a stepwise or stage process (USEPA, 1981, p. 4-32). The minimum diameter of a single-
pass plate tower is determined by using the gas velocity through the tower. If the gas velocity is too
great, liquid droplets are entrained, causing a condition known as priming . Priming occurs when
the gas velocity through the tower is so great that it causes liquid on one plate to foam and rise to
the plate above. Priming reduces absorber efficiency by inhibiting gas and liquid contact. For the
purpose of determining tower diameter, priming in a plate tower is analogous to the flooding point
in a packed tower. It determines the minimum acceptable diameter. The actual diameter should be
larger. The smallest allowable diameter for a plate tower is expressed by Equation 16.13:
d = Ψ[ Q g ) 0.5 ] 0.5
(16.13)
where
d = Plate tower diameter.
Ψ = Empirical correlation (m 0.25 hr) 0.25 /kg 0.25 ).
Q = Volumetric gas glow (m 3 /hr).
ρ g = Gas density (kg/m 3 ).
The term Ψ is an empirical correlation and is a function of both the tray spacing and the densities of
the gas and liquid streams. Values of Ψ shown in Table 16.2 are for a tray spacing of 61 cm (24 in.)
and a liquid specific gravity of 1.05. If the specific gravity of a liquid varies significantly from 1.05,
the values for Ψ in the table cannot be used.
Depending on operating conditions, trays are spaced at a minimum distance between plates to
allow the gas and liquid phases to separate before reaching the plate above. Trays should be spaced
to allow for easy maintenance and cleaning. Trays are normally spaced 45 to 70 cm (18 to 28 in.)
apart. In using the information in Table 16.2 for tray spacing different than 61-cm, a correction fac-
tor must be used. Figure 16.10 is used to determine the correction factor that is multiplied by the
estimated diameter. Example 16.5 illustrates how the minimum diameter of a tray tower absorber
is estimated.
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