CBEN 408 Quiz #4
Name (1 point): __________________________________
April 4, 2016
You may consult with your classmates. Express results to at least two significant digits.
1. (1point) In an amine acid gas absorption unit is the amount of acid gas absorbed most
depend on:
a. The lean loading.
b. The rich loading.
c. The sum of these loadings.
d. The difference between these loadings.
e. All of the above.
f. None of the above.
You want to treat 100 MMscfd gas containing 20 mol% CO2 to an exit concentration of 2
mol%. You can circulate 18 wt% MEA to do this. The lean loading will be 0.10 mol acid gas
per mol amine & the rich loading cannot exceed 0.45 mol acid gas per mol amine.
2. (3 points) How much CO2 will be absorbed [lb.mol/day]?
3. (2 points) How much MEA is needed [lb.mol/day]? (Just the amine, not the total
solvent.)
4. (3 points) You find out you can only circulate half as much needed solvent. What will be
the CO2 content of the treated gas [mol%]?
Solution
1. C, the difference between the two
2. The hydrocarbon content of the gas is 80 MMscfd (since it is 80 mol% of the gas). The
rate of treated gas will be:
80 MMscfd
=
N out = 81.63 MMscfd ,
0.98
the rate of CO2 out is:
=
N CO2,out
81.63 MMscfd )( 0.02)
(=
So the amount absorbed is:
1.63 MMscfd ,
N CO2,abs =
N CO2,in M N CO2,out =
20 M 1.63 =
18.37 MMscfd ⇒ 48,400 lb.mol/day ,
3. The rate of amine needed is:
=
N MEA
N CO2,abs
48,400
=
= 138,000 lb.mol/day .
Rrich M Rlean 0.45 M 0.1
4. Half the amine rate will absorb half the amount of CO2. So, instead of absorbing 8.16
MMscfd it will only absorb 9.18 MMscfd, letting 10.81 MMscfd leave. So, the new CO2
content will be:
=
yCO2
10.81
= 0.119 ⇒ 12 mol% .
80 + 10.81