Today, and what you need to know, we're going to talk about that detail working of a power plant. In particular, I'm going to use the example of the Abbott Power Plant at the University of Illinois. This power plant was created to make both some electricity for campus, originally all the electricity, and also steam to heat the buildings. Whenever you can do this type of combined process, where you can make electricity and use the waste heat not just to exhaust to the air or ultimately through a cooling tower, but use the buildings of the campus or of a city as the cooling tower, as the thing that takes away the waste heat, you're way ahead of the game. So let's first talk about how to burn coal. For many years coal was the only source of energy input for the Abbott Power Plant. Today, they've added a new gas turbine, but the coal system is still one of the most fascinating. If we look back in time, how did people first burn coal? Well, they had a fairly simple arrangement of some type of boiler, and there was a door, and you had a person, all right, and they shoveled coal into the burning pile. Great! This might be the guy on the train that's actually putting the coal into the train, it might be the person in a boat putting the coal into the big boilers. Now to make coal burn, you need a lot of air. So there is another part of this, right? There's got to be some grate, or a hole here, or something so that you've got airflow. We need the oxygen, right? The oxygen is going to turn the carbon into carbon dioxide, and there has to be some place where the smoke can get out. Well that's great. We've now got air, we've now got smoke, but how are we actually making any power out of this? The key to that is that the walls are made out of water. Huh? How do you make a wall out of water? Well, OK. What you basically have is a pipe system. The walls on the outside are basically made of some types of pipes, piping system, so that the water flows in, and out comes steam. So the water boils while it's in the process of being in these piping system and all the outside edges of the boiler, because after all, in the middle of the boiler you've got all this fire, all this flame. The boiler boils the water. The smoke goes through. The air comes in, and you have somebody, the stoker, shoveling in the coal. That's great! It works, but it's not very efficient. At some point we've got to turn off the fire, and we have to take out the part of the coal that didn't burn, the ash. And you've got to have burst in there, and you've got the door open, all sorts of problems. So you might imagine that modern mechanization can fix that. Somewhere in the '20s, they came up with the mechanical stoker, and this system is still in use today at the Abbott Power Plant. These boilers themselves were put in I think in the early 1940s, but basically it's mid-20s technology. And the key in this technology is a moving grate. What do I mean by moving grate? Imagine the treads of a tank. This is a mesh, sort of like a chain-link fence that's moving around going here in this diagram, to the right. Somewhere up here we have a coil hopper. We've got chunks of coal falling in to the system. And because the grate is moving the coal moves along with it. The beauty of this system is that we have a gap here, and this gap allows the burnt coal, the ash, to fall off the end of the moving grate. And you time the movement of the grate, it's slow. I mean it's moving about, like... even slower than that, but it's timed just right so that the amount of coal you're adding, by the time the coal gets to here, all of the energy content ideally has been spent. We still need air. So there is a large vent system. So air is being constantly blown through the grate, and of course there's still going to be a smokestack. And the smoke is going to go up here. We do the same thing in terms of the boiler to make the water. The walls of this, in the back walls, are all tubes of water. These tubes of water boil and turn into steam. The fire is very hot. This whole area is burning, and we can use coal more efficiently because we can control the length of time it's in there. We can collect the ash automatically by simply using gravity, '20s technology. The technology used still in the coal burners at the Abbott power plant. Technology didn't stay there. One of the problems with this system is that the ash still has quite a bit of unburned coal in it. We want to squeeze every last bit of energy out, and we actually want to make the recovery system for pollution maybe even a little easier. We can do that by crushing the coal first, pulverising it, and in this way if there are large inclusions in the coal, things that don't burn, rocks or maybe a large inclusion of sulfur for instance, it can be screened out. The coal crushes much more easily than the other pieces of material that would be embedded in it. So then, we can take this, and we can actually make a cyclone burner. Let me show you the top view first. So the top view of this cyclone burner looks something like this. And the air and the coal dust, the coal dust plus the air, comes in in this manner along the edge. So it makes this type of cyclone shape. The advantage of this, is that the parts that don't burn are a little heavier. They're not burring, there's a piece of rock that's going around in a circle, so it gets thrown off to the sides. And now if I draw the view of this from the side view, I get something like this - the air is swirling around, all of the ash collects on the edges because of that cyclone nature and can fall out in ash chute at the bottom. And my smoke goes up the top. I can get more complete combustion with this, and I'm a few steps ahead on getting rid of the sulfur and other impurities that would otherwise have just turned into the smoke. Now, the cyclone burner is not the end-all of coal. This tends to burn very, very hot, so hot that the nitrogen that's in the air can sometimes make more nitrous oxides. So while we might have done better on some of the fly ash control, we're probably doing a little worse and making more things that could turn into acid rain. The next evolution of power plants is fluidized bed.
