[SOUND] So, what we have so far in burning coal, is we've got a way to make steam, capture the heat, feed the coal in and take out the large pieces of ash, the ones that don't fly up in the air. But you can imagine how fine coal dust is. And that must mean how fine some of the ash, which might be on the order of 10% of the coal, is as well. That ash is so fine that it flies around in the air. It's not settled out by gravity. And we call it fly ash. A really long chimney, a really long smoke stack, can be effective because some of that, by the time it has to go up such a huge height, might fall back down. But mostly large smoke stacks are effective because they take the pollution that's coming out of them and raise it high above the area where the power plant it. And that way, it doesn't settle back down until you're outside the city, or maybe it falls down on someone else's city. Or if you're in a crowded place like Europe, maybe it falls down on someone else's country. There should be a better way than just a tall smokestack to get rid of your particulate fly ash pollution, and there is. A very widely used technique is with an electrostatic precipitator. Now, what is an electrostatic precipitator? We're basically going to take panels. All right, I'm trying to draw in 3D here a whole series of panels, metal sheets. And these metal sheets are going to be charged. We'll put an electric charge on them. That creates an electric field between the gaps. The smoke is going to come up through the gaps. Because the particles in the smoke, the very fine fly ash, will pick up an electric charge when they move through an electric field, they will be attracted and they will stick to the panels. And the air that continues to come up now, that will go to my chimney, is not quite as dirty. Actually, it's much less dirty. Of course, all this ash is going to continue to build up, and to build up, and to build up. And at some point, it'll be about ready to fall off. In fact, if you didn't do anything to get the ash off those panels, this would work for a half hour and then stop working. Because as much ash would be coming off into the stream of air going by as ash was sticking to it in the first place. So, what they do is they have a big hammer. Seriously. [LAUGH] A big hammer that hits the panels. And when the hammer hits the panels, [SOUND], right? All that ash falls into some type of hopper at the bottom. And just like the other things, the cross-section of these is shaped something like this. And you can see from these pictures of the large electrostatic precipitators at the Abbott Power Plant, large rectangular metal boxes shake down to the bottom so that the ash can be collected. And inside are series of plates that are charged up. And this is a great way to get the fly ash out of the coal. Well, we haven't done anything yet to get rid of the actual molecular components, the sulphur dioxide that's going to go up the smoke stack. You could use coal if it has no sulphur. It's much more expensive and there isn't much of it around in the world, by comparison to the coal that does have sulphur. On a periodic table, sulphur is right under oxygen. Just like carbon can turn into carbon dioxide, sulphur can turn into sulphur dioxide. There's energy content there. You're actually burning the sulphur. The problem is sulphur dioxide can be very unfriendly. Sulfur dioxide itself isn't the culprit. The culprit is when sulfur dioxide sticks to a small grain of dust in the air where there's more oxygen, and turns into sulfur trioxide, SO3. When SO3 hits water, it turns to sulfuric acid. This is a problem. because let's say you are breathing the exhaust from a coal power plant. You're not sitting on top of the smoke stock going, [SOUND], right? But you're somewhere in town or somewhere nearby and that air is the air that you're breathing. So, do we have particles? Yes, the electrostatic precipitator isn't perfect. Do we have sulfur dioxide? Yes, the coal coming with 3% sulphur. So, when I have fly ash particles, sulphur dioxide, that means I'm going to make little dust particles, dry acid precipitate it's called, that has the sulphite ion on it, SO3. When you breath it, where's the first place it finds water? On your lung tissue. So, guess what? You've just made sulfuric acid in your lungs. How does that feel? Not very good. Or when the dry acid precipitate falls to the ground and hits the dew, maybe on top of your nice shiny new car, this happened once at the Abbott Power Plant. There was something that went wrong in the pollution control system, so for a small amount of time, the pollution control system wasn't operating. The flue gases were going right up through the chimney, and I think maybe the precipitator wasn't working at the time either, so you had bigger chunks of fly ash. They go up. They are now coated with sulphite. Their morning dew is on the cars. The dry acid precipitate, I'm not talking about hail stone type pieces, right? I'm just talking about sand type pieces, right? Fall down, coat the cars. Every place where there is a dew drop has now turned into a sulfuric acid puddle. Suddenly everybody had cars that looked like leopard spots. Nice black car, all sorts of white spots. The university had to paint a lot of cars that day. So, dry acid precipitate is not a good healthy thing. We want to get rid of the sulphur. And a huge amount of efforts at a modern power plant are used to get rid of the sulphur. The most efficient way, and the way in widest use, is called a scrubber. And a scrubber works on the principle that we're going to take some type of gravel, calcium carbonate, crushed gravel, so very simple, very cheap limestone, right? And we crush that up. And what we're going to want to do is, that we're going to want to bubble the sulfur dioxide through a combination of calcium carbonate and water. And this will create calcium sulfate. And of course we gotta get rid of the carbon, a little more CO2. Got to have a balanced equation, so maybe we need a little bit of air, oxygen from the air in the system too. This, of course, is what we're making anyway in the power plant, all right? All that carbon's turned into carbon dioxide. But we've managed to get rid of the sulfur dioxide. What is this? This is called gypsum. It's a stable, gypsum is a very inert type of chemical. If your walls in your house are made from wallboard, plaster board, that's what it is, it's made out of gypsum. So, it's not toxic, I mean, I wouldn't just go eat a ton of it, but it's kind of a chalky-like substance, and you can bury it. You can landfill it and put it back in the coal mine. This process maybe is simple here, but mechanically you've gotta actually do something to make this work. So, a scrubber system takes the crushed limestone and water slurry and all of the exhaust from the power plant after the electrostatic preceptors washes through it. And it washes through it on the surface area of all those bubbles, or maybe you actually have the gas going through and you spray this sulfur, this water solution in, right? In some way you get the gas in contact with the liquid. The liquid that contains the calcium, the water that contains the calcium carbonate and you form this gypsum. And the gypsum does not dissolve. So, it falls to the bottom, you pump out this water with the gypsum in it, put it through some filter, separate out the solids from the liquids, return the water back to the system. And you have converted sulphur dioxide to an innocuous solid compound. [MUSIC]
