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  • Getting to Green

    An administrator pushes, on a shoestring budget, to move his university and the world toward a more sustainable equilibrium.

Sequestration reality check
February 4, 2010 - 8:52pm

The last time I did algebra in these pages, I crashed and burned. But the compulsion, triggered by President Obama's latest proposal that your dollars and mine be invested in making "clean coal" a reality, is just too strong. Plus, I'm a slow learner.

So let's start with some basic facts:

In the USA, coal is burned almost exclusively for the purpose of generating electricity; it puts about 1950 million metric tons of CO2 (or 520 mmt of carbon) into the atmosphere every year.

A metric ton of CO2, at sea level and at 32 degrees Fahrenheit, takes up about 18000 cubic feet. Do the multiplication, and the CO2 that would need to be sequestered (captured and stored) every year to make burning coal a clean process would fill about 35 trillion cubic feet. That's a layer of CO2 which would cover the entire surface of the country (including Alaska, remember) to a depth of about 4 inches. In 9 years, that adds up to three feet. In a century, it's the height of a 3-story building. Across the entire USA. Where and how are we going to store that much stuff? How are we going to be sure that it won't ever escape into the atmosphere? What are we smoking, to be even thinking about this?

Of course, most of the weight and volume of the CO2 comes not from carbon (the coal), but from oxygen (the air). If we could somehow separate the two (strip out the carbon), the oxygen could go back into the atmosphere without creating a problem. Plants do that (transform CO2 into O2 plus hydrocarbons) all the time. An acre of forest converts (depending on a number of variables) enough CO2 to create between one and two metric tons of carbon per year. So, what we'd need to create would be a processing capacity equivalent to about 350 million acres of forest. That's about twice the size of Texas, and it would require an amount of energy equivalent to all the sunlight those trees would absorb. And we'd still have to find a way to store the carbon extracted, which would be about equal in volume to all the coal burned to create it.

None of which is to say that the infrastructure and the logistical processes to burn coal and not contribute to global warming can't happen. But it does demonstrate that to make it happen, we'd have to more than trade away the advantage -- low cost -- that's causing our electrical companies to want to burn coal in the first place. "Clean coal" may be technologically feasible (I'm not saying it is, I'm just saying I can't prove a negative), but it's clearly not economically feasible. And it's even more clearly not economically attractive when compared to renewable technologies which are considered "too expensive" today.

I used to do consulting work to a manufacturing company which was known for its engineering culture. In that organization, it was common practice for engineers to low-ball initial cost estimates by an order of magnitude or more, on the basis that "if we told management what it's really going to cost, they'd never let us go forward with the project."

Compared to the proponents of "clean coal", those engineers were entirely scrupulous in their honesty.


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