| 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. _____________________________________________
|
Posts Tagged ‘training seminar’
Coal Power Plant Fundamentals – The Generator
Monday, March 7th, 2011
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.
_____________________________________________
|
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. _____________________________________________ |
Coal Power Plant Fundamentals – Coal Handling
Sunday, January 30th, 2011| If you’ve ever read a book to a small child on the subject of food or digestion, you’ve probably come across the analogy that our stomachs are like a furnace and our digestive system much like an engine. We explain to the youngster that what we eat is important, because our body needs the right fuel in order to operate properly. If little Susie or Danny insisted on eating only candy day after day, their bodies would become weak and sick.
In much the same way a coal power plant is like a living organism, eating fuel in order to function. But instead of meats and vegetables, it eats coal, and the coal handling department of a power plant acts as a dinner table. It’s where the food is placed and prepared before it enters the diner’s mouth. The coal our power plants consume comes from one of two places, underground mines or strip mines. It all depends on the particular geology of the area from which the coal is harvested. According to the US Energy Information Administration, underground mines are more common in the eastern United States, while strip mines are more common in the western states. The coal from underground mines is excavated by means of shafts and tunnels which are dug deep beneath the earth’s surface in order to provide access to the buried coal deposits. In strip mines the deposits are just below the surface, so the topsoil is merely stripped away with heavy earthmoving machinery, like bulldozers, to reveal the coal. In both types of mining activity excavating machines and conveyors are required to remove the coal from the mine so it can be loaded for shipment to its ultimate destination. Once harvested, coal is shipped to power plants primarily by train, river barge, or ship. Its journey can cover thousands of miles. It culminates in delivery to a power plant, where it is unloaded by means of a huge piece of machinery called a rotary dumper. This machine is capable of grabbing onto 100 ton railcars and turning them upside down. The coal spills into a large collection hopper positioned next to the railroad track. If the coal has found its way to a plant located near a waterway, that means of transport was most likely have been made by flat barge or ship. In this case a large crane with a clamshell bucket is used for unloading. The crane drops its bucket into a pile of coal located within the ship’s hold, takes out a large bite, then hoists and dumps its contents into a large collection hopper next to the crane. To get an idea of how coal flows within the coal handling system of a power plant, let’s refer to the flow chart in Figure 1.
Figure 1 – Schematic Diagram of the Coal Handling System Collection hoppers and have slanted bottoms which allow coal to easily spill out onto a conveyor belt. Within the plant coal is transported by means of conveyors into what’s known as a “breaker building.” This building lives up to its name because it contains a very large machine whose job it is to break the chunks of raw coal that have been harvested from mines into smaller chunks which the boiler can work with. Once broken down, the coal will go to one of two places, either directly into silos or coal bunkers in the power plant building for short term storage, or into an outside storage pile, usually a prominent feature of a power plant due to its formidable size. The coal pile can be several stories tall and much larger than a football field. It acts as a reserve supply should the regular delivery of coal be interrupted by labor strike, natural disaster, or equipment failure. When necessary, the coal is removed from the pile and sent into the plant to fill the coal silos. Coal from the silos is used to feed the power plant boilers. Next week we’ll continue to follow coal’s journey, on its way to arguably one of the most important pieces of equipment in a power plant, the boiler. _____________________________________________
|
Coal Power Plant Fundamentals
Sunday, January 23rd, 2011| Several years ago I was asked by power producers within the electric utility industry to write and then present a training course on the subject of coal power plant fundamentals. The finished product was a two day introductory course on the energy transformation process within a coal fired plant.
Since that time my seminar, entitled Coal Power Plant Fundamentals, has been presented to a variety of audiences, including Mirant Corporation, Platte River Power Authority, and Integrys Energy Group, Inc. Audience makeup has been diverse and has included equipment manufacturers, mining companies, power industry consultants, and regulatory agencies. This seminar, which I continue to present today in meeting rooms across the country, covers all major systems in a typical power plant, from coal handling when the coal first enters the plant, to its eventual end destination, the electrical switch yard which facilitates power transmission to customers. My Power Point presentation is embellished with ample illustrations, including photographs that I have taken during the course of my career and diagrams which I created using CAD, or Computer Aided Drawing software, one of which is featured below. In addition to the overhead slides, I provide a 150-page bound book which is distributed to seminar attendees. They use it to both follow along with my lecture and have a source of refresher material to take home with them. I’ve been told that having my illustrations in front of them makes a world of difference towards their understanding of the subject matter. The unique thing about my course is that it focuses on the simplified presentation of complex engineering concepts, much like my blogs do. Of course it always helps to have an engineering background or scientific background of sorts, but I wrote the course to accommodate understanding of the subject matter by individuals without any technical background. Accountants, salespersons, administrative staff, plant operating and maintenance workers, and journalists have all found the course to be easy to follow, interesting, and informative. So how do you get electricity from coal? To answer this question and give you a sampling of my seminar material let’s take a look at Figure 1.
Figure 1 – The Coal Power Plant Energy Transformation Process Following along from left to right, the coal is first burned in order to transform the chemical energy which it contains into heat energy. That heat energy is then absorbed by water inside a nearby boiler, where it is converted into steam. The heat energy in the steam flows through a pipe into a steam turbine where it is again transformed, this time into mechanical energy that enables the turbine shaft to spin. The mechanical energy in the turbine is then transmitted by its shaft, enabling it to turn an electrical generator. And, finally, the mechanical energy is transformed by the generator into electrical energy for our usage. Simple process, right? Well, maybe, maybe not. My illustration certainly helped to simplify things, but there are a lot of details that were purposely omitted so as not to “muddy the waters.” It’s those details which have the potential to make things a lot more complicated, and next week we’ll begin to take a closer look at some of them. _____________________________________________
|
