Alright, here's a dumb question that I've pondered on for a while: If capturing CO2 from the atmosphere is so difficult, why aren't we capturing it where it is produced, at the exhaust? Impractical? More impractical than the former? Or just impossible?
There are a number of capture projects doing what you suggest on full scale power plants and other industrial facilities. And yes you are right, its cheaper to catch it at a point source than in the atmosphere.
The projects work by circulating chemicals through the smokestack that latch onto the CO2 in the flue gas. The chemical is then heated up to remove the CO2 which is then pumped underground where it is sequestered, hopefully forever. The chemical is recycled back to the smokestack for the process to begin again.
When working well such systems capture around 80% of the CO2 at a energy penalty of around 20%. The problem is that the system rarely work well, so in the real world those numbers aren't achieved. This is why there are relatively few such systems deployed in the world despite $Bs in subsidies spent.
Lately, oil companies have been feeling the pressure to show results on this, so there are a lot of projects that have gone into development.
