by Monte Davis
12+16+16 = 44. We can all agree on that.
44/12 = 3 2/3. Good so far?
That’s all the math needed to ask some pointed questions about CCS. That stands for carbon capture and storage (or “sequestration”), a technology discussed and explored at pilot-project scale for decades. Its goal is to separate and collect the carbon dioxide from combustion, before it is released into the atmosphere, then put it in very long term storage so it doesn’t contribute to further climate change. So CCS is really CO2 capture and storage – and the difference between carbon and carbon dioxide is where the arithmetic above comes in.
Carbon’s atomic mass is 12; oxygen’s is 16. (Never mind isotopes.) So combining a carbon atom and two oxygen atoms – combustion — yields a molecular mass for CO2 of 44… or 3 2/3 times that of the “unburnt” carbon atom. These numbers are ratios, so the math is the same for any units: completely burn 12 grams of pure carbon, and get 44 grams of CO2; burn 12 million tons, get 44 million tons of CO2. Fossil fuels aren’t pure carbon, of course, and combustion rarely burns every bit of what there is, so the emission ratio varies. Coal typically yields 2.1 times its mass in CO2; firewood, 1.6 to 1.8 times; gasoline, 2.3 times; natural gas, about 2.8 times.
Pause here, because this is deeply counterintuitive – so deeply that we don’t realize it. We’ve had chemistry for a few centuries, arithmetic for millennia. But we’ve been using fire deliberately for a million or two years, seeing the aftermath of wildfire for much longer. All that experience taught us in our bones that the ashes always weigh less than the fuel did. As for the smoke – why, just look at it! Any hominid can see that it weighs nothing at all!
Because CO2 swirls invisibly away with that smoke, and soon mixes with the air and dissipates, we’ve learned only in the latest eyeblink of time to account for all the combustion products. It takes an effort to grasp that CO2 is as much “ash” as the gray powder in the fireplace – ash that weighs more than the logs we burned. The 15 gallons of gasoline in your car’s tank weigh about 100 pounds. When it’s gone, you’ve made a present to the world of about 230 pounds of carbon dioxide, along with much smaller quantities of carbon monoxide, benzene, 1,3-butadiene, etc. Read more »