EGEE 101
Energy and the Environment

Sequestration: Part 1

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Sequestration is locking something away. With CO2 we wish to lock it away so it does not enter the atmosphere and contribute to climate change (possibly). So all we need is a location where high volumes of CO2 can be stored–trivial, right?

There are not too many locations where there are massive holes in the ground, but there are other options:

  • In the ocean
  • In minerals
  • In depleted oil and gas wells
  • In brine fields
  • In coal fields (unmineable)
  • In carbon Sinks
 Graphic representation of flue gas.
Flue gas: Nitrogen is blue, water is red with two white hydrogen atoms attached, carbon dioxide is gray with two purple spheres attached, there is some oxygen too. The where is Waldo question? Can you spot the single S atom (yellow)?
Credit: JPM

Most will be used in the US where appropriate. However, there is a significant and costly catch: we do not get pure carbon dioxide out of the stack of power plants! What goes in: fuel and air. What comes out: products of combustion and air. The products of combustion are mostly carbon dioxide and water with lesser quantities of NOx and sulfur dioxide, etc. The air that we used is where the problem is. Air is mostly nitrogen. We want the oxygen but have to let the nitrogen tag along unless we can afford to separate them (\$\$\$\$\$\$). For every 1 mole of oxygen, we get about 6 moles of nitrogen. We also add more air than is necessary to help the mixing process, necessary for combustion to take place. So the nitrogen that goes into the system comes out again and we will have to separate the carbon dioxide from the other gases, oxygen (from the excess air), water (product of combustion), and nitrogen (\$\$\$\$\$\$). In the flue gas image shown to the right, the molecules are shown very close together in an unrealistic representation (too high a density) for viewability.

We have the technology, but part of the cost of sequestration will be this separation process. If we did not separate the gases, we will have to pay more for the compression, transportation, and pumping (\$\$\$\$\$\$).

Watch the (4:46) video below. It is a good simulation overview of the carbon capture and storage approach.

Very simplistic overview of carbon capture and storage.