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Electricity Generation From Coal
Early Origins of the Coal-Fired Electric Power Plant • The Reciprocating Steam Engine uses the action of steam to move a piston in a sealed chamber • The modern version was developed first by James Watt during the 1760 s • This would later be used to power the first coal power plants www. history. rochester. edu
The First Practical Coal-Fired Electric Power Plant Pearl Street Power Station – New York City • Built by Thomas Edison • Opened Sept. 1882 • Used to power Edison’s incandescent electric lighting http: //ieeexplore. ieee. org/iel 5 /8014/26956/01197918. pdf? a rnumber=1197918 http: //www. ieee-virtual-museum. org
The Process • Coal was used to heat water in boiler room pipes to produce steam • The steam was used in a reciprocating (piston) steam engine to produce mechanical energy • The mechanical energy was converted into electricity by a dynamo (generator) Inside the dynamo room www. nps. gov
Limitations of the Pearl Street Generating Station • Generated low voltage direct current 1. 2. 3. Area of Manhattan powered by Pearl Street Plant (1 mi^2) http: //www. ieee-virtual-museum. org This resulted in high power line losses that necessitated in having a small service radius Along with that, voltages could not be stepped up or stepped down. This allows the transmission of electricity to occur at very high voltages over long distances and step down for municipal use. The high voltage allows a low current for the same amount of power which greatly reduces I^2 R losses
Model of the Pearl Street Plant
The Steam Turbine A turbine in the Penn State Coal Power Plant http: //www. psu. edu/ur/archives/inter com_2003/Feb 20/gallery. html • Invented by Charles A Parsons in 1884 • Replaced the reciprocating steam engine because it was more efficient • First station to use them exclusively for power generation was the Fisk Street Station of Chicago in 1903 • Generates more than 80% of the world’s power today
Pulverized Coal Pulverized coal burner • • Introduced in 1917 The process of burning it brought advantages that included 1. a higher combustion temperature 2. Improved thermal efficiency 3. and a lower requirement for excess air for combustion http: //www. rst 2. edu/ties/acidrain/IEcoal/how. htm
Cyclone Furnace • Introduced in 1942 by the Babcock & Wilcox Company • Allowed for the combustion of poorer grades of coal (with higher moisture and ash contents) with less ash production and greater overall efficiency.
Modern History of Coal Power • Due to competition with alternate power sources such as oil and nuclear power along with stricter environmental legislation; coal’s share of electricity production would drop by 10% from 1965 to 1975 • Several events would reverse this trend
Important Events to the Modern Coal Power Industry http: //memory. loc. gov/master/pnp/ppmsca/03400/03433 u. tif • Clean Air Act of 1970 and the 1977 amendments slowed the growth of the industry • Oil shortages and price increases in 1973 -1974 made oil a much less economically viable alternative to coal (oil fuel cost went up from 80 cents to 1. 93 dollars per million Btu from 1973 to 74) • Natural Gas price increases also made it less economically viable as a fuel
Coal’s Geographic Shift • • www. jstor. org In 1970, 93% of US bituminous and lignite coal was mined east of the Mississippi In 1990 it was only 61%
Coal’s Geographic Shift (Continued) • Wyoming is now the nation’s biggest coal producer with 30% of the nations production in 2002 1. This is primarily because Wyoming coal’s low sulfur content helps power plants meet their emissions requirements 2. This in recent years has left the transportation system of the region strained because it was not built to handle the massive amounts of coal train traffic Powder River Basin of Wyoming • Because of the lack of railroad capacity, many power plants fail to receive a consistent supply of coal
Powerplants by fuel type in 2005 http: //www. eia. doe. gov/cneaf/electricity/epa_sum. html
Electricity Generation From Coal • Let’s start at the beginning. • Almost everything in our homes and businesses today run on electricity. • That electricity has to come from somewhere. • Some sources of electricity are nuclear power, solar power, wind power, and most important for us Coal Power.
Electricity Generation • Electricity as we know it doesn’t just come out of the ground, it has to be generated. • In all types of power plants the electricity is generated in the same manner; a prime mover turns a rotor covered in electrical windings inside a magnetic field. The magnetic lines of flux are cut by the conducting wires inducing current in the wires. • Rotor turns at 3600 RPM which induces current at 60 Hz in the United States.
Stator Windings Hitachi. co
Stator Casing Ece. umr. edu
Steam Turbine • As mentioned before, something has to turn the rotor in order to generate electricity. • In our case the prime mover happens to be a steam turbine. • Steam comes out of the tubes in the boiler and into a manifold then into the turbine. • As the steam passes over the turbine blades, torque is produced as a result of the blade shape.
Steam Turbine Wikipedia
Turbine Generator and Condenser
Steam Turbine • The rate of steam flow controls how fast the turbine rotates and therefore the frequency of the electricity produced. • As the steam moves through the turbine energy is extracted which results in a pressure drop. • Therefore the LP turbine is located at the exit of the HP turbine to extract the maximum amount of energy from the steam before it is sent to the condenser. • As electricity is generated it leaves the building though a very large circuit breaker and a series of transformers before it enters the power grid.
Path of Electricity
Condenser • After the steam leaves the LP turbine it travels to the condenser, where it is condensed back to liquid water. • The condenser is a heat exchanger that cools the steam while is passes over tubes that have cold water running through them. • The cold water removes energy from the heated steam causing it to condense which is necessary for the water to be re-used as feed. • There is another reason why the condenser is necessary which we will discuss shortly.
Cooling Towers • The water that runs through the tubes in the condenser must be cooled down in order to condense the steam. • This is accomplished using very large cooling towers, in which the water is atomized by sprayers and cooled down by atmospheric conditions and fans. • The substance leaving cooling towers is sometimes mistaken for smoke, but it is in fact just water vapor.
Main Condenser Holte International
Feed System • After the condensate is collected in the hotwell of the condenser it is pumped through the feed system. • The feed pump increases the pressure of the feed water in order for it to flow back into the boiler to be turned back into steam to start the cycle over again. • This stage turns out to be the 4 th and final stage of something called a heat engine.
Basic Heat Engine • A heat engine operates on the principle that during the conversion of heat from a hot reservoir (boiler tubes) to a cold reservoir (condenser/cooling tower) there must be work done to satisfy the 1 st and 2 nd laws of Thermodynamics. • As mentioned before, a heat engine consists of four stages: Generation, Expansion, Condensation, and Feed.
Basic Heat Engine
Laws of Thermodynamics • 1 st: “The increase in internal energy of a system is equal to the amount of heat energy added to the system minus the work done by the system on the surroundings. ”
Laws of Thermodynamics • 2 nd: The temperature differences between systems in contact with each other tend to even out and that work can be obtained from these non-equilibrium differences, but that loss of heat occurs, in the form of entropy, when work is done. • 2 nd: It is impossible to produce work in the surroundings using a cyclic process connected to a single heat reservoir (Kelvin, 1851).
Laws of Thermodynamics • The second law also states that the maximum efficiency of a heat engine can be determined by: η = 1 -(Th/Tc) • Efficiency is also equal to the work output over the heat input. η = Δ W/Δ QH
Efficiency • An ordinary power plant operates between the temperatures of 565 C and 25 C which leads to maximum efficiency of around 64%. • However, due to the losses mentioned earlier the usual observed efficiency is about 35%. • This shows how much of the energy stored in the coal is just wasted instead of being converted to electricity.
Steam Cycle • The previous part of the presentation was to explain the process behind electricity generation that occurs after the coal portion. • I will now go through some of the components dealing with the coal aspect of the power plant ending at the boiler which is where the steam cycle began. • Most of what I will discuss is particular to the Co-gen plant that I visited.
Coal Delivery • After the coal is mined and loaded into trucks it is delivered into chutes that lead to the Bradford Breaker. • The breaker is a drum with hammers in it that rotates and breaks the coal down into pieces about 4” diameter, which fall through the screen and onto the conveyor belt which leads to the storage facility.
Bradford Breaker www. penncrusher. com
Coal Storage • After the coal has been sufficiently reduced in size, it enters a storage facility, in this case, a large dome. • The coal is then stacked using a machine you will see in the next slide, which rotates and places the coal around the perimeter of the dome. • This same machine also takes coal from the pile and delivers it to the crusher building.
Crusher • The coal is delivered from the storage facility to a device conveniently called a coal crusher. • This machine takes the 4” pieces of coal and through a series of rollers converts the fuel into a fine powder. • This powder is necessary for proper combustion in the boilers. • All newer state of the art power plants are set up to work with pulverized coal, but older plants may operate with lumped coal.
Fuel Feed System • The conveyor belt delivers the crushed coal to a series of fuel feeders, which inject coal into the boilers along with a mixture of high pressure air for combustion.
Boilers • The final stage for the coal coincides with the first stage of the steam plant. • The boiler is usually the largest component of the coal power plant climbing as high as 200 ft. • Inside the boilers the pulverized coal is burned while it more or less floats with the aid of HP air. • Lining the entire inside of the boiler are tubes which carry the feed water to be turned into steam.
Boilers www. boatnerd. com
Inside the Boiler news. minnesota. publicradio. org
After the Boiler • As the coal is burned a large amount of ash is produced. • Some falls to the bottom and is collected, then mixed with water and sent to the ash pile. • Very light ash particles also escape with the exhaust gasses which are captured by a bag filter system. • This fly ash is collected in a silo until a certain level is reached when it is pumped to the ash pile via HP air.
Fly Ash www. concretethinker. com
Ash • This ash has a basic p. H and has some beneficial uses. • After a truck delivers coal to the plant it is filled with ash to return to the reclamation site. • The high p. H helps treat acid mine drainage.
Ash • The fly ash is used as a substitute to make Portland cement. • Another use of fly ash is structural fill for highway embankments and the fill under new highways.
Exhaust Gasses and the Stack • One of the most controversial aspects of a coal power plant is what comes out of the stack. • During the combustion process dangerous gasses and particulates are released, such as NOx, SOx, and CO 2. • Controls are in effect for each of these in new plants, however older plants spew thousands of pounds of each of these into the atmosphere every year.
Exhaust Gasses and the Stack
The Stack www. industcards. com/as-pontes. jpg
Coal Power • This concludes the component tour of the coal power plant. • I will now talk about parallels of coal power with alternatives like nuclear power.
Coal vs Nuclear Power • Both coal and nuclear power plants operate on the same principle of using steam to spin a turbine generator to make electricity. • The entire steam cycle is exactly the same the only difference lies in the heat source
Nuclear Power • The reactor heats primary water due to heat released in fission as well as the diffusion of neutrons escaping the core. • This very hot primary water travels to the steam generator where the secondary water is converted to steam. • From there everything is the same as we just went through.
Works Cited • • • • A History of Power Clientship. " Sargent & Lundy. 2006. Sargent & Lundy. 8 Dec 2006