Page 123 - Gas Purification 5E

Alhnolamines for Hjidrogen Surfide and Carbon Dioxide Removal 1 13

Table 2-1 3
Trays vs. Packing in Selective Treating with 50% MDEA Solution

Field Data Calculated Data
14 Valve Trays 14 Valve Trays 30 ft of Pall Rings (2")

Feed Gas
Pressure, psia 915 915 915
CO?, vol% 4.0 4.0 4.0
HIS, ~01% 0.4 0.4 0.4
Product Gas
H:SI ppmv 8-12 11.2 2.57
co:, volC/c. 1.8-2.2 1.85 3.05
C02 slip, % 45-55 45.1 75.2
Temperature Bulge
Location mid-tower mid-tower
Temperature,"F 171 1%
Rich Solvent
Moles C02/mole amine 0.597 0.273
Moles H2S/mole amine 0.1094 0.1094
Moles acid gas/mole amine 0.706 0.382
Source: Vickery et 01.. 1988

Figure 2-79 is a highly simplified chart for estimating the required diameters for tray-type
amine plant contactors. Similar charts are provided by Maddox (1985). Manning and
Thompson (1991) suggest using the Souders-Brown equation (Chapter 1, equation 1-22)
with an empirical constant of 0.25, reducing the gas velocity by 25 to 35% to avoid jet flood-
ing and by 158 to allow for foaming. They also suggest limiting the liquid velocity in the
downcomers to 0.25 ft/sec.
The stripping column diameter can be determined by the same procedures as used for the
absorber. Maddox (1985) provides approximate diameter (and height or len,$h) requirements
for the stripping column and other regeneration system vessels as a function of the amine
solution flow rate.

Column Height

Experience-Based Height Determination

Column heights for amine plant absorbers and strippers are usually established on the basis
of experience with similar plants. Almost all installations that utilize primary or secondary
amines for essentially complete acid gas removal are designed with about 20 trays (or a
packed height equivalent to 20 trays) in the absorber. In bulk acid gas removal applications,
experience has shown that if a 20-tray column is supplied with sufficient amine so that the
rich solvent leaving the absorber has an acid gas loading that is 75 to 80% of the equilibrium
value, then the amine on the upper 5 to 10 absorber trays is very close to equilibrium with the