Archive for the ‘power plant training’ Category

Superheating, Part I

Monday, August 19th, 2013

      Last time we learned that our power plant boiler as presently designed doesn’t do a good job of producing ample amounts of superheated steam, the kind of steam that turbines need to spin and power generators.   During the process of superheating the more heat energy that’s added to the steam in our boiler, the higher its temperature becomes.   However, our boiler can only produce a limited amount of superheated steam as it stands now.

Engineering expert witness power plant

      So how do we get more heat energy into the superheated steam?   Take a look at the illustration below for the solution to the problem.

coal fired power plant expert witness

      You’ll note a prominent new addition to our illustration.   It’s called a superheater.

      The superheater performs the function of raising the temperature of the steam produced in our boiler to the incredibly high temperatures required to run steam turbines and electrical generators down the line, as explained in my blog on steam turbines.   The superheater adds more heat energy to the steam than the boiler can alone.

      In fact, the amount of heat energy in the superheated steam produced with our new design is proportional to the amount of electrical energy that power plant generators produce.   Its addition to our setup will result in more energy supplied to the turbine, which in turn spins the generator.   The result is more electricity for consumers to use and a more efficiently operating power plant.

      But inefficiency isn’t the only problem addressed by the superheater.   We’ll see what else it can do next week.

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Heat Energy Within the Power Plant— Water and Steam Cycle, Part 2

Wednesday, August 14th, 2013

      Last time we learned that electric utility power plants must have water treatment systems in place to remove contaminants from incoming feed water before it can be used.   This clarified water is then fed to a boiler by the boiler feed pump as shown below.

utility power plant expert

      As it stands this setup will work to provide electricity, however in this state it’s both inefficient and wasteful.   We’ll see why in a minute.

      Boilers, as their name implies, do a great job of heating water to boiling point to produce steam.   They do this by adding the heat energy produced by burning fuel, such as coal, to water, then steam.   We learned in earlier blogs in this series that the energy used to heat water to boiling point temperature is known as sensible heat, whereas the heat energy used to produce steam is known as latent heat.   The key distinction between these two phases is that during sensible heating there is a rise in temperature, during latent heating there is not.   For a review on this, see this blog article.

      When water starts to heat inside the boiler, sensible heat energy is said to be added.   This is represented by phase A of the graph below.

power plant expert

      During A, heat energy will raise the temperature of the water to boiling point.   As the water continues to boil in phase B, water is transforming into steam.   During this phase latent heat energy is said to be added, and the temperature will remain at boiling point.

      In phase C something new takes place.  The temperature rises beyond boiling point and only steam is present.   This is known as superheated steam.   For example, if the boiler pressure is at 1,500 pounds per square inch, steam becomes superheated at temperatures greater than 600°F.

      Unfortunately, boilers alone do a poor job of superheating steam, that is, continuing to raise the temperature of the steam present in phase C.   This is evident by the fact that phase C is quite small in comparison to phases A and B before it.   This inefficiency in producing ample amounts of superheated steam results in a small amount of useful energy being provided to the turbine down the line, which is bad, because steam turbines require exclusively superheated steam to run the generator.

      Next time we’ll see how to provide our steam turbine with more of what it needs to run the generator, more superheated steam.

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Heat Energy Within the Power Plant – Water and Steam Cycle, Part 1

Monday, August 5th, 2013

      Last time we learned that electric utility power plant boilers are vessels that are reinforced with thick steel and are closed off from the surrounding atmosphere so as to facilitate the building up of highly pressurized steam.   This steam is laden with sensible heat energy, meaning it’s a useful energy, and it’s used to run steam turbines, which in turn drive electrical generators.   The end result is power to consumers.

      Let’s now revisit our basic electric utility boiler diagram to see how water and steam flow.

Electric Utility Power Plant

      Water is fed into the boiler, heat is applied externally, and steam exits through a pipe leading to the steam turbine.   You’ll notice that after the steam passes through the turbine, some of it is expelled into the surrounding atmosphere.

      Since water is being continuously boiled off to produce steam, the boiler must be continuously replenished with a fresh supply.   This is typically supplied by a nearby body of water, hence one reason that power plants are often situated on a lake or river.

      Since water contains both minerals and organic matter, including algae, a treatment system to remove these contaminants must be added to the water’s inlet area before it can be used.   This will keep operating parts such as the boiler and turbine free of damaging deposits.

electric utility power plant boiler and steam turbine

      The treatment system operates much like the water softener in your home, but on a larger scale.   Lake water is drawn into the system by a make-up pump, so named because it makes up, or replenishes spent water with a fresh supply.   The result is clean, mineral-free water that’s delivered to the boiler by a boiler feed pump, so named because its specific function is to feed water to the boiler.

      Feeding water to the boiler on a continuous basis is no easy task because of the steam straining to break free, and boiler feed pumps are massively powerful devices built to accomplish this.   They effectively force water into the boiler even as high internal pressures try to force the water out.   This pressure is often greater than 1,500 pounds per square inch (PSI) in modern power plants.

      So at this point we’ve discussed the fact that the boiler requires a continuous supply of fresh water, which is converted into high pressure steam, which is then sent on to spin a steam turbine.   The turbine powers an electrical generator, resulting in usable energy.

      If you’ve been reading along closely, you will have identified that as things stand now it’s a rather inefficient and wasteful system, a point which we’ll address in next week’s blog.

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Heat Energy Within the Power Plant—The Power Behind the Turbines

Monday, July 29th, 2013

      Last time we discovered that the boiling point of water varies.   It’s dependent upon the amount of pressure exerted on its surface, which varies due to a variety of reasons, including where it is in relation to sea level.   Before we see what happens under higher than atmospheric pressures, such as exist in an electric utility power plant boiler, let’s cover some basics.

      In the power plant, water is heated in a boiler specifically to produce steam, unlike our tea kettle where the primary purpose is to produce hot water.   The steam produced is used to spin turbine generators, which in turn generate electricity, as I explained in a previous blog on steam turbines.

      Unlike a tea kettle, which is open to the atmosphere on your kitchen stove, the boiler in a power plant is an enclosed, reinforced steel vessel.   See illustration below.

coal power plant expert

      The reinforced steel boiler vessel is designed to withstand great internal pressure as temperatures rise within.   In addition to providing a safety feature, the enclosed space provides a sheltered environment for collecting steam so it can later be put to use spinning power generating turbines down the line.   In other words, surface water inside the boiler is closed off from the surrounding atmosphere, allowing its internal pressure to build for our specific purposes.

      As heat energy is added to water within the boiler, the water boils and steam bubbles break out from its surface, filling the empty space above the surface with pressurized steam.   This steam will try to expand here, but it can’t, because it’s being constrained by the reinforced steel vessel within which it is enclosed.   Instead, steam pressure builds up on the surface of the water inside the boiler until it is high enough to be released through an attached pipe which is connected to a nearby turbine.

      We’ll talk more about this pent-up energy and how it is put to use within the power plant in next week’s blog.

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Forms of Heat Energy – Boiling Water and Atmospheric Pressure

Sunday, July 21st, 2013

      If you’ve ever baked from a pre-packaged cake or cookie mix, you’ve probably noticed the warning that baking times will vary.   That’s because the elevation of the area in which you’re doing the baking makes a difference in the baking time required.   Living in New Orleans?   Then you’re at or below sea level.   In Colorado?   Then you’re above sea level.   Your cake will be in the oven more or less time at the prescribed temp, depending on your location.

      Last time we learned how the heat energy absorbed by water determines whether it exists in one of the three states of matter, gas, liquid, or solid.   We also learned that at the atmospheric pressure present at sea level, which is about 14.7 pounds per square inch (PSI), the boiling point of water is 212°F.   At sea level there are 14.7 pounds of air pressure bearing down on every square inch of water surface.   Again, I said sea level for a reason.

      The boiling point of water, just like cake batter baking times, is dependent upon the amount of pressure that’s being exerted on its surface from the surrounding atmosphere.   When heat energy is absorbed, it causes the water or cake batter molecules to move around.   In fact, the temperature measured is a reflection of this molecular movement.   As more heat energy is absorbed, the molecules move more and more rapidly, causing temperature to increase.

      When the water temperature in our tea kettle reaches its boiling point of 212°F at sea level, the steam molecules in the bubbles that form have enough energy to overcome the atmospheric pressure on the surface of the water.  They become airborne and escape in the form of steam.

boiler

      If we’re up in the Rockies at say an altitude of 7000 feet above sea level, the atmospheric pressure is only about 10.8 PSI.   There’s just less air up there.   That means there’s less air pressure resting upon the surface of the water, so it’s far easier for steam molecules to form into bubbles and leave the surface.   As a result the boiling point is much lower in the Rockies than it is at sea level, 196°F versus 212°F.

utility boiler expert

     So what if the water was boiling in an environment that had even higher pressures exerted upon it than just atmospheric?   We’ll see how to put this pent-up energy to good use next week, when we begin our discussion on how steam is used within electric utility power plants.

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Forms of Heat Energy – Latent

Monday, July 15th, 2013

      If you took high school chemistry, you learned that water is created when two gases, hydrogen and oxygen are combined.   You may have even been lucky enough to have a teacher who was able to perform this magical transformation live during class.

      Depending primarily on the amount of heat energy absorbed, water exists in one of the three states of matter, gas, liquid, or solid.   Its states also depend on surrounding atmospheric pressure, but more about that later.    For our discussion, the water will reside at the atmospheric pressure present at sea level, which is around 14.7 pounds per square inch.

      Last time we learned that the heat energy absorbed by water before it begins to boil inside our example tea kettle is known as sensible heat within the field of thermodynamics.   The more sensible heat that’s applied, the more the water temperature rises, but only up to a point.

      The boiling point of water is 212°F.    In fact this is the maximum temperature it will achieve, no matter how much heat energy is applied to it.   That’s because once this temperature is reached water begins to change its state of matter so that it becomes steam.   At this point the energy absorbed by the water is said to become the latent heat of vaporization, that is, the energy absorbed by the water becomes latent, or masked to the naked eye, because it is working behind the scenes to transform the water into steam.

      As the water in a tea kettle is transformed into steam, it expands and escapes through the spout, producing that familiar shrill whistle.   But what if we prevented the steam from dispersing into the environment and continued to add heat energy?   Ironically enough, under these conditions temperature would continue to rise, upwards of 1500°F, if the stove’s burner were powerful enough.   This process is known as superheating.   Now hold your hats on, because even more ironically, the heat added to this superheated steam is also said to be sensible heat.

      Confused?    Let’s take a look at the graph below to clear things up.

power plant engineering

      Sensible heat is heat energy that’s added to water, H2O, in its liquid state.   It’s also the term used to describe the heat energy added to steam that’s held within a captive environment, such as takes place during superheating.    On the other hand, the latent heat of vaporization, that is the heat energy that’s applied to water once it’s reached boiling point, does not lead to a further rise in temperature, as least as measured by a thermometer.

      Next time we’ll see how surrounding air pressure affects water’s transition from liquid to steam.

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Forms of Heat Energy – Sensible

Sunday, July 7th, 2013
      In our house the whistle of a tea kettle is heard throughout the day, no matter the temp outside.  So what produces that familiar high pitched sound?

sensible heat power plant boiler

      When a tea kettle filled with room temperature water, say about 70°F, is heating on the stove top, the heat energy from the burner flame will transfer to the water in the kettle and its temperature will steadily rise.  This heat energy that is absorbed by the water before it begins to boil is known as sensible heat in thermodynamics.  To read more about thermodynamics, click on this hyperlink to one of my previous blog articles on the topic.

      So, why is it called sensible heat? It’s so named because it seems to make sense.  The term was first used in the early 19th Century by some of the first engineers who were working on the development of boilers and steam engines to power factories and railways.  Simply stated, it’s sensible to assume that the more heat you add to the water in the kettle, the more its temperature will rise.

      So how high will the temperature rise?  Is there a point when it will cease to rise?  Good questions.  We’ll answer them next week, along with a discussion on another form of heat energy known as the latent heat of vaporization.

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Coal Power Plant Fundamentals – The Generator

Monday, March 7th, 2011
     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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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.

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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.

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