Absorption - Introduction to Carbon Capture and Sequestration - page 166

these ideas by designing a sample carbon capture separation using pure
water as a solvent. CO 2 and N 2 have different solubilities, and water is
cheap and readily available (assuming we can get it from sources like the
ocean). At least in theory, water appears to be an ideal solvent. We will
revisit this issue several times later in the chapter, starting with Box 5.1.1
[5.2, 5.3].
The next step is to ask what happens when you apply this technology
to a coal-fi red power plant. As we discussed earlier, this type of plant is
the most logical point source for carbon capture systems based on effi -
ciency. But if you look at a generic 500 MW power plant, we're talking
about a lot of CO 2 — 70 × 10 8 g per day. That equates to a rate of about
4,000,000 m 3 /day! And there are additional restrictions for the technol-
ogy at a capture site, such as the requirement that the equipment fi ts on
the site of the power plant. Clearly, improving absorption design will be
a huge factor in successfully translating this technology to practical car-
bon capture systems.
Box 5.1.1 The problem with water
We start talking about CO 2 absorption by looking at water as a solvent. After all, water
is all around us, and it is used in many other industrial processes, including cooling,
mining, fuel production, and emissions control. The reality, however, is not so simple.
In addition to its use for drinking and agriculture, water is required to produce most
forms of energy, including that generated by turbines, hydroelectric, and geothermal
methods. Particularly when it comes to drinkable, or potable, water, there are great
strains on our current global resources. Further complicating matters, energy is required
to move, treat, deliver, use, and dispose of water. The inexorable relationship between
water and energy generation even has a name: the water-energy nexus [5.2, 5.3].
The global consumption of both water and energy is on the rise. According to the
World Health Organization, as much as one-sixth of the world's population does not
have access to safe drinking water. Yet in most countries, more water is consumed for
energy purposes than for drinking. In the USA, for example, electricity production in
2000 accounted for 39% of national freshwater withdrawals. As the population
increases, our energy needs will put an even greater strain on our water resources. As
we think about how to minimize the costs of absorption for carbon capture in order to
make it a sustainable process, we will need to look at both water and energy as two
sides of the same coin. It would not make sense for carbon capture technology to
trade one form of environmental strain (CO 2 ) for another (H 2 O).
( Continued )