| When I was a kid I remember how cool it was to have a headlight on my bike. Unlike the headlights that the other kids had, mine was not powered with flashlight batteries. The power came from a little gadget with a small wheel that rode on the front tire. As I pedaled along, the tire’s spinning caused the small wheel to spin, and voila, the headlight bulb came to life. Little did I know that this gadget was a simple form of electrical generator, and of course I was oblivious to the fact that a similar device, albeit on a much larger scale, was being used at a nearby power plant to send electricity to my home.
Over the last few weeks we learned how a coal fired power plant transforms chemical energy stored in coal into heat energy and then into mechanical energy which enables a steam turbine shaft to spin. We’ll now turn our attention to the electrical generator. It’s responsible for performing the last step in the energy conversion process, that is, it converts mechanical energy from the steam turbine into the desired end product, electrical energy for our use. It represents the culmination in energy’s journey through the power plant, the process by which energy contained in a lump of coal is transformed into electricity. To show how this final energy conversion process works, let’s look at Figure 1, a simplified illustration of an electrical generator.
Figure 1 – A Basic Electrical Generator You’ll note that the generator in our illustration has a shaft with a loop of wire attached to it. When the shaft spins, so does the loop. The shaft and wire loop are placed between the north (N) and south (S) poles of a horseshoe magnet. It’s a permanent magnet, so it always has invisible lines of magnetic flux traveling between its two poles. These magnetic lines of flux are the same type as the ones created by kids’ magnets, when they play with watching paperclips jump up to meet the magnet. The properties of magnets are not completely understood, even to adults who work with them every day. And what could be more mysterious than the fact that as the shaft and wire loop spin through the lines of magnetic flux in the generator, an electric current is produced in the wire loop. Now, this current that’s flowing through the spinning wire loop is of no use if we can’t channel it out of the generator. The wire loop is spinning vigorously, so you can’t directly connect the ends of the loop to stationary wires. A special treatment is required. Each end of the loop is connected to a slip ring. A part called a “brush” presses against each slip ring to make electrical contact. The electrical current then flows from the loop through the spinning slip rings, through the brushes, and into the stationary wires. So, if, for example, a light bulb is connected to the other end of the stationary wires, this completes an electric circuit through which current can flow. The light bulb will glow as long as the generator shaft keeps spinning and the wire loop keeps passing through the magnetic lines of flux from the magnet. So we see that the key to the whole energy conversion process is to have movement between magnetic lines of flux and a loop of wire. As long as this movement occurs, the electricity will flow. This basic principle is the same in a coal fired power plant, but the electrical generator is far more complicated in construction and operation than shown here. My Coal Power Plant Fundamentals seminar goes into far greater detail on this and other aspects of electricity generation, but what I have shared with you above will give you a basic understanding of how they operate. That concludes our journal with coal through the power plant. This series of blogs has, you will remember, presented a simplified version of the complex material presented in my teaching seminars. Next week we’ll branch off, taking a look at why electrical wires come in different thicknesses. _____________________________________________
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Posts Tagged ‘electric utility training’
Coal Power Plant Fundamentals – The Generator
Monday, March 7th, 2011
Coal Power Plant Fundamentals – “Big Coal”
Sunday, February 27th, 2011|
We’ve been talking about coal fired power plants for some time now, and it’s always good to introduce third party information on subject matter in order to gain the most from the discussion. What follows is an excerpt of an interesting book review on the subject of coal consumption which appeared in the New York Times: There is perhaps no greater act of denial in modern life than sticking a plug into an electric outlet. No thinking person can eat a hamburger without knowing it was once a cow, or drink water from the tap without recognizing, at least dimly, that its journey began in some distant reservoir. Electricity is different. Fully sanitized of any hint of its origins, it pours out of the socket almost like magic. In his new book, Jeff Goodell breaks the spell with a single number: 20. That’s how many pounds of coal each person in the United States consumes, on average, every day to keep the electricity flowing. Despite its outdated image, coal generates half of our electricity, far more than any other source. Demand keeps rising, thanks in part to our appetite for new electronic gadgets and appliances; with nuclear power on hold and natural gas supplies tightening, coal’s importance is only going to increase. As Goodell puts it, “our shiny white iPod economy is propped up by dirty black rocks.” To read the entire article, follow this link: http://www.nytimes.com/2006/06/25/books/review/25powell.html?_r=2
A locomotive crane unloading coal from railcars at a power plant in the late 1930s. Next week we’ll continue our regular series, following energy’s journey through the power plant. _____________________________________________ |
Coal Power Plant Fundamentals – The Steam Turbine
Sunday, February 20th, 2011|
When I was a kid I didn’t have video games or cable TV to help me occupy my time. Back then parents tended to be frugal, and the few games I had were cheap to buy and simple in operation, like the plastic toy windmill I’d play with for hours on end. All I had to do to make it spin was take a deep breath, pucker my lips together, fill my cheeks with breath, then blow hard into the windmill blades. Its spin was fascinating to watch. Little did I know that as an adult I would come to work with a much larger and complex version of it, in the form of a power plant’s steam turbine. You see, when you trap breath within bulging cheeks and then squeeze your cheek muscles together, you actually create a pressurized environment. This air pressure buildup transfers energy from your mouth muscles into the trapped breath within your mouth, so that when you open your lips to release the breath through your puckered lips, the pressurized energy is converted into kinetic energy, a/k/a the energy of movement. The breath molecules flow at high speed from your lips to the toy windmill’s blades, and as they come into contact with the blades their energy is transferred to them, causing the blades to move. A similar process takes place in the coal power plant, where steam from a boiler takes the place of pressurized breath and a steam turbine takes the place of the toy windmill. If you recall from my previous article, the heat energy released by burning coal is transferred to water in the boiler, turning it to steam. This steam leaves the boiler under great pressure, causing it to travel through pipe to the steam turbine, as shown in Figure 1.
Figure 1 – A Basic Steam Turbine and Generator In A Coal Fired Power Plant At its most basic level the inside of a steam turbine looks much like our toy windmill, of course on a much larger scale, and it is very appropriately called a “wheel.” See Figure 2.
Figure 2 – A Very Basic Steam Turbine Wheel The wheel is mounted on a shaft and has numerous blades. It makes use of the pressurized steam that has made its way to it from the boiler. This steam has ultimately passed through a nozzle in the turbine that is directed towards the blades on the wheel. This is the point at which heat energy in the steam is converted into kinetic energy. The steam shoots out of the nozzle at high speed, coming into contact with the blades and transferring energy to them, which causes the turbine shaft to spin. The turbine shaft is connected to a generator, so the generator spins as well. Finally, the spinning generator converts the mechanical energy from the turbine into electrical energy. In actuality, most coal power plant steam turbines have more than one wheel and there are many nozzles. The blades are also more numerous and complex in shape in order to maximize the energy transfer from the steam to the wheels. My Coal Power Plant Fundamentals seminar goes into far greater detail on this and other aspects of steam turbines, but what I have shared with you above will give you a basic understanding of how they operate. So to sum it all up, the steam turbine’s job is to convert the heat energy of steam into mechanical energy capable of spinning the electrical generator. Next time we’ll see how the generator works to complete the last step in the energy conversion process, that is, conversion of mechanical energy into electrical energy. _____________________________________________ |
Coal Power Plant Fundamentals – Combustion
Sunday, February 13th, 2011| Ever have a small child threaten to hold his breath until he passes out and he actually managed to do it? It’s not that unusual. And if his body were prevented from acting in self preservation, that is, taking in breaths while he was unconscious, leading to his eventual awakening, he would die. While the human body can survive about a month without eating and three days without water, under normal conditions it can survive only a matter of minutes without breathing. Power plants, too, require oxygen to function, and this process is called combustion.
Human lungs, along with the diaphragm which works to expand and release the lung cavities, enable our bodies to breathe in air, then expel the waste product, carbon dioxide. Oxygen is needed to metabolize, that is burn, our food, enabling the food cells’ energy to be absorbed by our bodies and converted into energy to live. Like us, coal power plants need to breathe in oxygen in order to convert coal’s latent energy into a usable form. Previously we learned how coal is fed to a coal mill where it is pulverized into a fine powder. This powder is then sucked out of the mill by the exhauster and blown through a serpentine path of pipes leading to the burners on the furnace. The burners will then act upon the coal, combining it with the oxygen in our atmosphere to create a chemical reaction capable of releasing coal’s energy in the form of heat. All this activity looks to a bystander like a massive, sustained fire in the furnace. See Figure l.
Figure 1 – Coal Power Plant Combustion The boiler is contained within the furnace and is situated so it is exposed to fire from the combustion process. Heat energy from the fire transfers into the water in the boiler, much like when you boil water for tea in a kettle on your stovetop. If you’ve ever boiled water, you know that once it gets hot enough it will turn into steam, and the same for our furnace boiler. The steam emitting from the boiler will cause a turbine-generator to spin, and the end result will be electricity for our use. In the simple diagram of Figure 1, waste products from the combustion process, like carbon dioxide, go up the smoke stack and are released into the atmosphere. Incidentally, this is the same type of carbon dioxide that we exhale from our bodies when we breathe. Please keep in mind that Figure 1 is a very simplified diagram. In reality waste products leaving the furnace go through various pollution control devices where most pollutants are removed before they reach the smoke stack. These details, and many more, are the type of information that would be covered during my training seminar, Coal Power Plant Fundamentals. Next time we’ll learn how the heat energy in steam is converted into mechanical energy capable of spinning a turbine generator to make electricity.
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Coal Power Plant Fundamentals – Feeding The Furnace
Sunday, February 6th, 2011| Today we’ll continue our discussion of coal’s journey through a power plant. Keep in mind that the material presented in this series of blogs is meant to be a primer. It is a simplification of what actually goes on. My training seminars go into much more depth.
Now imagine a five course meal spread out on the table before you. You load up your plate and pack a forkful of food into your mouth. You instinctively chew, getting the digestive process underway and making it easier to swallow. Power plants approach their consumption of coal in much the same way. Last time we talked about handling the coal and filling up silos for short term storage within the power plant building. The coal silo is analogous to a dinner plate, and the furnace, which heats up the boiler water to make steam for the turbine, acts very much like a diner’s stomach. As for the fork and your teeth, there are a couple of machines within power plants which mimic their behavior. They’re called the coal feeder and coal mill. The coal feeder does as its name implies, it systematically feeds a measured amount of coal to the coal mill. The coal mill, also known as a pulverizer, then grinds the coal to make it easier for the furnace to burn it. Let’s take a look at Figure 1 below. At the top of the configuration is the coal silo, which is fully open at the bottom. Gravity draws the coal within the silo downward, facilitating the coal’s dropping through the opening into a chute, on its way to the coal feeder. The coal from the silo spills into little buckets on a wheel within the feeder, and as the wheel turns, the coal spills out and falls down into another chute leading to the mill.
Figure 1 – Feeding Coal To A Power Plant Furnace Now you could have the coal spill down a chute directly from the silo into the mill, bypassing the coal feeder entirely, but that’s really not a good idea. Just think how difficult it would be to chew if you tried to stuff an entire plate of food into your mouth at once. Just as your mouth requires to be fed in mouth-sized amounts, the coal mill must be fed coal in a size that it can handle. It’s the job of the spinning wheel inside the coal feeder to keep coal flowing in measured amounts to the mill. You see, the wheel is attached to a variable speed motor, and depending on how quickly the furnace needs to be fed, the wheel will either turn faster or slower. Once inside the mill, the coal is ground up before moving on to the furnace. The coal mill contains massive steel parts capable of pulverizing chunks of coal into a fine black powder. This pulverized coal is then propelled by means of an exhauster towards the burners. The exhauster sits next to the coal mill and both are often driven by the same electric motor. The exhauster is connected to the top of the mill by a pipe, and another pipe connects the exhauster to burners on the furnace. The exhauster acts like a big vacuum cleaner, sucking coal powder out of the mill, then blowing it through pipes leading to the burners. Finally, the powder ignites within the furnace, heating the water inside the boiler. Next time we’ll learn about the combustion process in the power plant furnace. _____________________________________________ |
