In President Bush’s 2006 State of the Union speech, he said, “To change how we power our homes and offices, we will invest more in zero-emission coal-fired plants, revolutionary solar and wind technologies, and clean, safe nuclear energy.” I thought I’d give a lay persons view of what this “zero-emission coal-fired power plant” actually is.
There may be other ways to do this, but in general, when politicians speak about zero-emission from coal, they’re talking about integrated gasification, combined cycle (IGCC) power plants. The whole process by which we get energy out of coal without any emissions at all is complex. There’s lot’s to do, and the details and infrastructure are definitely not completed. The U.S. is a leader in the commercialization of this technology, which is mostly led by GE.
Energy from coal
The first thing is to understand how we typically extract energy from coal. Coal is compressed plants, which are basically stored up solar energy from centuries and millennia. When we burn coal, we break down the hydrocarbon bonds, and the energy released in this reaction heats up steam in tubes lining the coal furnace. The steam then turns a turbine, and this rotating kinetic energy is converted to electricity and sent to the grid for you and me to power our computers and read this blog. A modern coal plant is about 40% efficient, by the way, which, it turns out, is very, very good. The very best solar cells are about 38%, and the photovoltaic kind that normal humans, who are not flying into space, can afford are around 17% (That’s from NREL, but I can’t find the original link)
The key point is that energy is stored in hydrogen-carbon bonds in coal.
Clean it before you burn it
Unfortunately, the black lumps we dig out the ground and call “coal” aren’t strictly hydrocarbons. After being buried for so long, the dried-up plants get mixed up with all manner of dirt. While we’re trying to get energy from the hydrogen-carbon bonds, these trace elements–for example, sulfur–get burnt up, and they form things like SO2 which causes smog and acid rain. There is mercury in there, and even radioactive elements too.
So one strategy, instead of just burning the coal, is to refine it first, like we do with crude oil. This refining process has been around for more than 50 years, but it’s finally becoming commercially feasible to do it for energy generation. The process, gasification, combines a slurry of coal powder with steam at high temperatures and pressures. The result is a thick slurry of everything that isn’t a hydrocarbon pouring out the bottom, and something called synthetic gas, or syngas, coming off the top. (I’m over-simplifying, but not too much…) Syngas is CO+H2. It’s very clean to burn; the result is water and CO2. An IGCC plant burns this syngas in a combustion turbine, which is essentially a jet engine, strapped to the ground. The kinetic energy from the rapidly turning jet engine turbine is converted to electricity and sent to the grid (of course, so that you can read this blog…).
Refining coal actually produces a lot of extra heat. This extra heat is used to produce steam which turns a steam turbine. This way, little of the energy from coal-gasification is wasted. That’s the “combined cycle” part of the process.
CO2 is a greenhouse gas!
We cleaned the coal before burning it, so there were no pollutants. We’ve got turbines turning, so we’re producing energy. Looks like everyone is happy. Not so fast. Burning syngas is clean, but as in any hydrocarbon combustion process, one of the end products is CO2. CO2 isn’t poisonous, and plants enjoy it plenty (They’ll combine it with water and solar energy to make new hydrocarbons.) but, alas, it traps more light than our atmosphere would normally do, if we’d stop fooling with it. Furthermore, loads of scientists now agree that too much CO2 in the air causes the planet to warm up like we’re in a giant greenhouse. So once we’re done commercializing IGCC, we’ve still got to figure out what to do with all the CO2.
It’s important to note here that Mr. Bush and many environmentalists have one thing in common: they all seem to think that because a fuel is renewable, like fuel from corn, that it’s good. Using bio-fuels is no answer to greenhouse gas production. Whether we get energy from burning plant products such as methanol or really old plant products such as coal, we still get CO2 as a by-product. Lots of it! The biggest difference between coal and methanol is that we don’t have to plant the coal.
What to do with the CO2
There’s really no good idea about what to do with all that CO2. Please don’t be disappointed when I tell you what the greatest minds on the planet think we should do with it. It does have a fancy name, though. Maybe that will make us feel better; it’s called CO2 sequestration. Basically we, um, bury it. We pump the CO2 into deep holes in the ground. We don’t know where all these holes are, but we know that we can use it to pump out oil, for example, and then just cap it off. We also think we can pump out huge underground cavities where there is water. We don’t actually know where all these giant aquifers are (because oil companies have spent more time looking for oil than for water, the greedy bastards), but I am sure we can find a few.
So somehow you’ve got to build your IGCC plant near one of these places to put the CO2, or you’ll have to build a pipeline to get it there. And we’ll have to be sure that these things stay tightly capped off, because if the CO2 leaks out, it won’t kill anybody right away, but the planet will warm up and bake just as sure as if we had never tried to get rid of the by-product in the first place. I’ll be honest, I am skeptical about CO2 sequestration. We can do it–we’ll have to–but we better not stop investing in other technology.
It’s good news that we can burn coal and have zero emissions. It’s good news, because as I’ve mentioned in previous posts, we have loads of coal in the United States. Amazingly, the syngas that is made in an IGCC plant can even be turned into diesel fuel to power cars, trains and airplanes! Yes, we can even power our existing transportation fleet with coal. The U.S. would be completely independent of foreign oil if we did that! (I should mention that using syngas for transportation does produce CO2, but it still beats being held over a barrel (pun intended) by a government that hates us.)
Except for one problem: we don’t have any IGCC plants right now. (That’s not strictly true, we have a few test plants, about five or so, and nobody is really doing CO2 sequestration yet.) That means we have to build them. Building a power plant isn’t free. Furthermore, IGCC plants aren’t any more efficient than other coal-fired power plants, so not only will we have to build a lot of them, but we won’t be getting any more energy out of each one, so the cost per kilowatt is going to have to go up-up-up. I don’t recall Mr. Bush mentioning this when he said we’ll invest in research.
Research is well and good, but will we and the U.S. or even world economy be able to pay for this zero-emission coal? I think we’ll have to, because the cost of cleaning up after all the hurricanes and floods caused by continued global warming will make up for it anyway, but we should be prepared for this drag on economic growth.
Where we’re going to get enough energy to keep the lights on is often a very complex issue. Let’s make sure that these important decisions aren’t made, well, in the dark!