Monday, October 26, 2009

The Clean Coal Situation

The moniker 'clean coal' has become a lightning rod for criticism. Liberals (and I am a liberal too) seem to think that clean coal technology is a joke, an obfuscation by greedy energy companies to make profits off warm and eco-friendly sounding names. The airwaves, these days, are saturated by ads (a) advocating clean coal technologies (b) claiming that there's no such thing as clean coal. Even the yes men (whom I usually appreciate) have gone on record claiming that there's no such thing as clean coal.

So, what is clean coal?

Let me summarize. A good place, of course, to start is the wikipedia page talking about clean coal.

Coal is dirty. It is basically carbon in its elemental form. When this carbon burns in oxygen, it forms IR trapping CO2. And that's why coal is dirty in the modern perspective.

Natural gas, on the other hand, is essentially methane. The good thing with methane is that one of the products of combustion is also water. Since methane consists of a significant amount of hydrogen, the amount of CO2 per unit Joule of energy produced is considerably less.

The idea behind clean coal is to use either of the following approaches

(1) Use pulverized coal (as is being done right now). But use a carbon capture mechanism in the flue gases. This can pose some issues, since the flue gases are typically at ambient pressure. This CO2 has to be captured, compressed, liquified, transported and sequestered.

(2) Use a coal gasification scheme, where the chemical energy is transferred from C to nH2 + mCO (a syngas). (A final goal is to make m = 0, converting all the C to CO2.) This CO2 can be concentrated BEFORE combustion itself (the second C in CCS). This is the idea behind the IGCC, and this is where I come in.

The fuel obtained from the coal gasifier contains a lot of hydrogen, and relatively less CO2. This results in a higher concentration of water vapor in the flue gases. Water vapor gas a higher thermal conductivity - and therefore results in a heavier thermal load on the blade. We need more aggressive cooling of the blade - and that's my hope for the future. This gives me a reason to keep on working on better cooling of turbine blades.

Neither of the two methods is economical right now. Things will of course should be different in a cap-n-trade regime. This method of sequestering produced carbon will of course add to costs - and this would never be able to compete with current fossil fuel based energy costs.

Now that you have all the CO2 that you have either sucked from the fuel before or after combustion. The kicker is, what does one do about it? How does one store this captured carbon?

One could do the obvious stuff like grow trees (especially in deserts), bury trees in landfills, create more landfills, have pet algae sucking in CO2... But that's not what I am interested in. I am interested in the more physical ways to sequester the carbon. And here's a few (which I glean from wikipedia...)

1. Put it in spent oil wells
2. Put it in acquifiers
3. Put it in underwater (though this might end up acidifying.the sea, destroying coral reefs and killing the fauna).

Let me agree with Harry Reid here. At this point in time there is indeed nothing called clean coal. There is something called 'cleaner-coal' technology. This technology might sound bad, but it is nothing to scoff at. While we cannot get rid of all CO2 from syngas (making m=0 is very, very tough), we can reduce carbon emissions significantly. We have this sobering reality:

Coal is actually one of the world's easiest fuels. It is available in large quantities in USA, India and China. India and China don't consume much energy per-capita at this point, but they're rapidly growing. Their energy needs are growing. Energy usage will increase in India and China - and that's a human rights necessity. (I expect India and China are representative of the developing world in general). It does not look like the usage of coal will decline on planet earth. It looks all set to increase. So, if we use coal, might as well ensure that the coal technologies under use are cleaner coal technologies rather than the current dirty coal technology.

And here's another point: rather than have politicians decide what works and what does not (an approach that has a success rate in single digit percentages), why not let the market do it? All the politicians have to do is, after all their internal bickering, come up with a Carbon trading scheme - or just a carbon tax - which will make apparent economic savings of clean coal in comparison with dirty coal. And then, the politicians can just take their hands of the wheel as far as climate change is concerned.

In conclusion, while people are right to ridicule current clean coal technologies, the future almost certainly has a place for clean coal, given the relative abundance of coal reserves in comparison with depleting petroleum reserves.

No comments: