Why Can’t We Just Burn Water?

1,099 dead coal miners agree: this sucksYou know what’s funny (besides comedy sketches I mean)? As a physicist who has been forced to study and has been tested on all the little tricks of thermodynamics, I’m not really sure why our society insists on heating water to produce electricity. The more I think about it the more I start to ask myself things like: what if we used a different material than water? And hey, doesn’t coal burn at a much higher temperature [~3,500°F (1’927°C)] than that at which water boils? Where does all that excess heat go? Could we maybe use something that boils at lower temperatures?

So first off, most electricity that is made from fossil fuels is produced by what are called thermal power stations, in which coal is heated, water is boiled, and steam is pressurized and forced through turbines at high pressure. Without the buildup of high pressure, these massive turbines wouldn’t move more than your grandma’s favorite wooden spoon does when you hold it over a boiling pot of spaghetti. That’s why we need high temperatures. Check out Gay-Lussac’s Law if you don’t believe me. The water vapor needs to be a super high temperature to create enough pressure to make giant steel turbines spin round and round. Thanks a lot, Joseph Louis Gay-Lussac.

But hey, water is quite useful in this scenario (also for drinking and a few other things). It’s used to drive massive turbines and also it acts as a coolant for the hot water that comes out of the turbine at like a bajillion degrees (or ~320°C, whatevs). So we have to use water. It’s cheap, it’s plentiful, it’s da bomb, yo!

So it dawns on me now that water and coal are the main ingredients for this process because of many many years worth of experimenting. Water has the a very flexibile set of properties that allow it to go through phase changes at relatively low temperatures without reacting chemically to everything inside of a power plant.

And coal — lovely lovely coal. It burns hotter and releases more energy than TNT, gunpowder, and wood; It doesn’t, however, release more energy than gasoline, compressed hydrogen, and Uranium-235—but none of those materials can be handled quite as easily nor can be found in such large quantities as coal can.

Once it’s out of the ground, it can be immediately burned, but is usually processed a bit first to remove some of the more hazardous, toxic, and corrosive things that dwell inside a chunk of coal—hydrochloric acid, ammonia, sulfur dioxide, and some (but not all) mercury. Coal is relatively non-reactive, but not always. Let’s not ignore those times when it is actually terribly and horribly reactive.

So coal and water are just the simplest solution. Coal is the most convenient thing to burn, and water is just the most convenient thing with which to absorb and to use that energy.

I have to admit that I do not like the idea of our society continuing to use coal for electrical power, but it is one of those cases where the “cold equations” seem to dictate its continued use. We burn and burn and burn coal, even though there are bad accidents, dirtied air and water, enormous amounts of CO2 churned into the atmosphere, and yes, lives lost. As a society, however, have decided that in this case, the positive outweighs the negative.

Thanks a lot, Joseph Louis Gay-Lussac.

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