Absorption - Introduction to Carbon Capture and Sequestration - page 183

Question 5.2.1 McCabe-Thiele to the limit
Given what we now know about the McCabe-Thiele diagrams, one question
that might have occurred to you is why not simply increase the n sol / n fl ue ratio
as much as possible?
is not too promising: 200,000 gallons of water per second
(to give some context, a typical shower uses 7 gallons per minute, so it
would take the equivalent of 2,000,000 showers to equal this volume per
second). Not only is that a lot of water, we must remember from the
absorber design (see Figure 5.2.1 ) where it is going: all the way to the
top of the absorber column. While fl ue gas is coming in at the bottom of
the absorption column, all that water must be pumped to the top of the
column before it comes down and then over to the stripper. Making mat-
ters worse, those 200,000 gallons per second of water must also be
heated in the stripper so that the CO 2 can be desorbed for storage. Some
useful numbers put this in context: 200,000 gallons per second equals
27,000 cubic feet per second. This equals ten times the Rio Grande river
in Texas or half of the Ganges river in India. Given all those energy
requirements, it's clear this system is not practical. We need another
idea. To look for a better solution, we move from the engineering per-
spective to the chemical perspective: how can we improve the driving
force for absorption?
Section 3
Solvent Design
Introduction
In our absorption column, the effectiveness of our separation is repre-
sented by the distance between our operating and equilibrium lines. In
order to drive mass transfer, we have two options: to increase the slope