Absorption - Introduction to Carbon Capture and Sequestration - page 224

(a) Adsorber using 30% MEA (b) Stripper using 30% MEA

equilibrium line
maximum mole fraction

minimum mole fraction
operating line

stages

0.14
0.12
0.10
0.08
0.06
0.04
0.02
0

Bottom

Top

0.80

0.60

0.40

0.20

Bottom

To p

0

0 0.005 0.001 0.0015

0 0.00002 0.00004

Mole fraction of CO 2 in a solvent (x) Mole fraction of CO 2 in a solvent (x)

Figure 5.8.4 McCabe-Thiele diagrams for MEA (2)
McCabe-Thiele diagrams for (a) an absorber with 33 stages operating at an L/V ratio of
11 and (b) a stripper with 27 stages operating at an L/V ratio of 51,000; both units are
using 30% MEA as the solvent and contain the same number of stages as used for the
water case in Figure 5.8.2 .

To estimate the economic advantage of switching from water to a
30% MEA solution, we calculated the capital cost associated with the
processes described above. We started by estimating the tray diameter
and spacing using the analysis provided by Seider et al . [5.17]. We cal-
culated the height of the column by multiplying the number of trays by
the tray spacing. We took into account the cost of sieve trays, the ves-
sels, ladders, and platforms using cost correlations corrected for the
present day (2012) cost index ( Table 5.8.1 ).
The overall cost is $3.32 million for the case in which water is the
solvent. When 30% MEA is the solvent, the cost is $941,775 when we
operate at the same L/V as used in the water case and $2.4 million when
we use the same number of trays as used in the water case. Hence, the
capital cost can be reduced by a factor of 3 by switching to 30% MEA
from water while keeping the same L/V conditions. The cost is driven
down primarily by the fact that we use a signifi cantly smaller number of
trays with 30% MEA than water. When we use the same number of trays
for both 30% MEA and water while changing the L/V ratio, we fi nd that
the capital cost drops marginally; we expect, however, that the utility