Total moles of acid gas absorbed ¼ 212:49 mol=h
Acid gas residual in the lean amine ¼ 57:37 mol=h
Total acid gas in grains=h ¼
269:87 Â 34 Â 16
0:0023
¼ 63:83 Â 10
6 grains=h
Total MEA solution ¼ 23,317gal=h
Then grains acid gas per gal of amine solution = 2,738 grains H 2 S/gal MEA.
From Fig. 2a for 20 % MEA solution, the H 2 S partial pressure is 0.33 psia.
Using the following equation, the absorption factor A is calculated:
A ¼
a 1 þ Rr
ð
Þ 1 À q
ð
Þ
pp=P
(11)
“a”is the mole fraction of H 2 S in feed gas ¼
212:5
3, 306:9
¼ 0:0643
R = mole MEA per mole acid gas absorbed = 3.0
r = 0.09 mole H 2 S per mole lean MEA
Then
A ¼
0:0643 Â 1 þ 3:0 Â 0:09
ð
Þ
f
g  1 À 2:45  10
À5
À
Á
È
É
0:33 Ä 335
¼ 82:1
Therefore
N ¼
log 1 Ä 2:45 Â 10
À5
À
Á Â 82:1 À 1
ð
Þ
È
É
log 82:1
¼
log 3:283 Â 10
6
À
Á
log 82:1
¼
6:5
1:91
¼ 3:4 theoretical trays
Set tray efficiency at 15 %; then actual number of trays = 23 (including reboiler).
MEA has a tendency to foam; therefore set tray spacing at 30 in (1.5 ft).
Then trayed section will have a height of 22 Â 1.5 ft = 33 ft.
Calculating the Contactor Diameter
Use foaming factor of 60 %.
Feed gas to the contactor is 30 MMscf/day.
Temperature of gas is 100
F and its pressure is 335 psia (these are average
conditions).
516
D.S.J. Jones and S.A. Treese