utdallas .edu /~metin Page 1 Electricity Generation Outline Combustion Generation Prof. Metin Çakanyıldırım used various resources to prepare this document for teaching/training. To use this in your own course/training, please obtain permission from Prof. Çakanyıldırım. If you find any inaccuracies, please contact [email protected] for corrections. Updated in Spring 2020
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Electricity Generation
Outline
Combustion
Generation
Prof. Metin Çakanyıldırım used various resources to prepare this document for teaching/training.
To use this in your own course/training, please obtain permission from Prof. Çakanyıldırım.
If you find any inaccuracies, please contact [email protected] for corrections.
Updated in Spring 2020
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Energy Generation ← Energy Transformation
✓ Solar energy → [Photovoltaics] → Electricity
▪ Kinetic energy → Electricity: Kinetic energy from the flow of
✓ Air flow @wind farms
✓ Water @hydroelectric plants
✓ Waves @oceans and tidal movements @coasts
▪ Hot Air/Steam
✓ Capturing thermal solar energy
✓ Performing nuclear reactions in nuclear plants
▪ Burning = combustion
▪ coal @coal-powered plants
▪ natural gas @gas-powered plants gas
▪ oil @oil-powered plants gas
Methods of Electrical Energy Generation
Energy resource (solar,nuclear, coal, gas, oil)
Kinetic energy
Combustion
Air/Steam flow by heat
Air flow by wind
Water flow by elevation
Electrical energy
Transformation
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Combustion and Efficiency
▪ Energy resource ∈ {Coal, Natural Gas, Oil}, pulverized versions
▪ Heat transfer medium ∈ {Air, Water, Carbondioxide}, supercritical versions
▪ Allam cycle with carbondioxide as heat transfer medium
▪ Coal power plants
▪ Pulverized coal
▪ Supercritical steam pulverized coal
▪ Heat rate, reciprocal of efficiency
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Kinetic & HeatEnergy
Turbine
Combuster
Cooler
Compressor
Kinetic & HeatEnergy
Kinetic & HeatEnergy
Air in the
pipes
Combustion Cycles: Brayton and Rankine▪ Single-phase medium: Heat warms up air ⇒ Pressure ↑. Hot air flows to turbines to rotate them.
▪ Low efficiency: 25%− 40%.
▪ Quick turn on/off.
TurbineCombuster
Compressor
Kinetic & HeatEnergy
▪ Two-phase medium: Heat boils the water into steam and also steam’s pressure ↑.
▪ Steam temperature ≈ 1000 oF and pressure ≈ 2000 psi (pounds per square inch).
▪ Efficiency ≈ 35% for plants of the 1970’s and ↑ ≈ 0.25 per year (roughly speaking).
▪ Efficiency is obtained at high temperatures ⇒ Turning on/off ↓ the efficiency.
▪ Frequent heating/cooling ⇒ Cracks & leaks of the thick metal vessels containing high-temperature steam.
Kinetic & HeatEnergy
Open Cycle: Air enters & leaves the system Brayton (closed) Cycle: Air enters & stays
Turbine
Combuster
Cooler
Compressor
Kinetic & HeatEnergy
Kinetic & HeatEnergy
Steam in
the pipesWater in
the pipes
Two-phase medium: Water + Steam
Rankine Cycle
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Combined Cycle Gas Turbine (CCGT)▪ Combined Cycle Turbine: 1st cycle is open cycle. Its output (hot exhaust gas/air) is used to boil water
in the 2nd cycle. The resulting steam is passed to a steam turbine.
▪ Efficiency ≈ 45% for plants of the 1980’s and ↑ ≈ 0.25 per year.
1st Cycle
2nd Cycle
1 2 3 2 Combuster
3 Turbine
1 Compressor
5 Cooler3
5
4
4 Heat exchanger
Open + Rankine Cycles
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Variation: Closed Cycle + Rankine Cycle
Turbine 1
Combuster
Cooler
Compressor
Kinetic & HeatEnergy
HeatEnergy
Turbine 2
Cooler
Compressor
HeatEnergy
Steam in
the pipes
Water in
the pipes
Air in the
pipes
HeatExchanger
Rotating shaft
Kinetic energy → Generator 1
Gas Turbine
Rotating shaft
Kinetic energy → Generator 2
Steam Turbine
Combined Cycle Turbines
Combined Heat and Power TurbineExhaust gas from power generation to heat homes
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New TechnologyAllam Cycle: Carbon Dioxide in Pipes
Combined Cycle
Gas & Steam in 2 Turbines
Allam Cycle: Carbondioxide in a Single TurbineCombusting natural gas with pure oxygenResults in supercritical CO2: 300 Atmosphere, 1150 oCSupercritical fluid advantages: ✓ A pump can pressurize it with far less energy than a
compressor needs to pressurize a gas. ✓ Its extra density ⇒ it efficiently gains & sheds heat.✓ Extra CO2 for EOR; extra H2O for watering✓ Sequestered emission & as efficient as combined cycleDesign disadvantages• Oxygen separation needs refrigeration• New turbine (length & angle of blades) design, by
Toshiba in 2012
▪ Allam Cycle prototype plant▪ First, 25MW in Houston, TX▪ Second, 50MW in La Porte, TX▪ See https://netpower.com
Based on R.F. Service. 2017. Goodbye smokestacks: Startup invents zero-emission fossil fuel power. Science,
appeared on May 24. DOI: 10.1126/science.aal1228
Note: Despite the title, Allam cycle is not zero-emission.
Another picture for CCGT
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Coal Power Plants
Coal provides 1 MMBtu at $4-5 or less.
– The price is relatively low. Except for the recently low priced natural gas price, coal is the cheapest energy
resource among fossil fuels.
Coal is abundant
– US reserves is 267,000 MM Ton and produces 1,131 MM Ton, so reserves will last at least 236 years.
➢ In addition to fuel costs, Capital cost and Operating costs: • Department of Energy uses 30 years lifetime to amortize costs below.
✓ $4.5 per million Btu ⇒ 9454 Btu costs $0.045. $0.045 = cost of coal fuel in 1 kWh.• Heat rate in financial context is [electricity output price]/[gas input price]. A ratio with no physical meaning.
• Burn up rate in a nuclear reactor is [energy output] / [weight of fuel input].
▪ Ex: An incandescent light of 60 Watt power is kept on day and night at a home. How much
energy does this bulb consume over a month?
▪ Ans: A month has 720 hours, the energy consumption is 720 × 60 = 43,200 Wh = 43.4 kWh
▪ Ex: A Christmas tree has 10 strands (strings) of light. Each strand requires 50 Watts. The tree is
lighted from 5 pm to 5 am over a month. How much energy does this tree consume over a month?
▪ Ans: Tree requires 10 × 50 = 500 Watts. It is lighted over 360 hours. Its monthly consumption is 360 ×500 = 180,000 Wh = 180 kWh
▪ Ex: A cloth washing machine is run on Mondays, Wednesdays and Fridays of each week for 80
minutes. Its power consumption is 900 Watt. How much energy does this washer consume over 4
weeks?
▪ Ans: The machine runs for 4 × 3 ×80
60= 16 hours in 4 weeks. It consumes 16 × 900 = 14,400 Wh =
14.4 kWh
▪ Ex: A cloth dryer runs with 4,000 Watt power and is operated on Mondays, Wednesdays and
Fridays of each week for 90 minutes. How much energy does this dryer consume over 4 weeks?
▪ Ans: The machine runs for 4 × 3 ×90
60= 18 hours in 4 weeks. It consumes 18 × 4,000 = 72,000Wh =
72 kWh
▪ Ex: A central air conditioner requires 12,000 Watts. In a summer month, it runs in cycles of 4
minutes of operation and 11 minutes of idling throughout each day. How much energy does this
AC consume over a summer month?
▪ Ans: A month has 720 hours, the AC is operates for 720 ×4
4+11= 192 hours. Its monthly energy
consumption is 192 × 12,000 = 2,304,000Wh = 2,304 kWh
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Electric Energy Kinetic EnergySingle-phase Generator
Faraday’s law: Changing magnetic field induce flow of electrons on conductors.▪ If a charge 𝑞 moves in a magnetic field 𝐵 with speed 𝑣, it experiences force with magnitude 𝑞𝑣𝐵
and with direction perpendicular to both 𝐵 and 𝑣. Moving charge ⇒ Force.
▪ Reverse: Force ⇒ Moving charge. Use force to change magnetic field (magnitude & direction).
▪ Rather than moving the conductor (charge), move (rotate) the magnet (magnetic field):
S N
S N
Vo
ltag
e
1,1
1,2 1,3
1,4 2,1
Conductor
Magnet
Fig
ure
s ar
e bas
ed o
n F
igure
2-1
of
Ele
ctri
c
Pow
er S
yste
m B
asi
cs b
y S
teven
W. B
lum
e,
Publi
shed
in 2
007 b
y I
EE
E P
ress
.Time
A voltage cycle
Force
Cycle #, Quarter #
Another
cycle
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Frequencies ofRotor vs. Voltage
S N
S N
1,1
1,2 1,3
1,4 2,1
Rotor: Magnet and the shaft; rotor rotates.
Rotating the rotor twice faster increases frequency by a factor of 2.
– Frequency of rotor in steam turbines: 30-60 revolutions per second.
– Voltage has 60 cycles per second in the USA, i.e., 60 hertz.
Gray voltage curve is from the previous page. Blue is twice as frequent (fast) as gray.
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Multi-polar Rotors toFrequency of Rotor ↑ Frequency of Voltage
1,1
1,2 1,3
1,4 2,1
60 hertz frequency does not necessarily mean 60 rps (revolutions per second) for the rotor.
– Water is dense and water turbines rotate at a low frequency: Hoover Dam rotors have 3 rps.
60 hertz voltage can be obtained with quadrupolar rotor rotating at 30 rps.
1 revolution of rotor ⇒ 2 voltage cycles with a quadrupolar rotor.
N
N
Ex: Hoover Dam rotors have 3 rps, how many poles should be on the rotor to obtain 60 hertz voltage?
– Ans: 2 poles (N & S) yield 3 hertz; 4 poles (2N & 2S) yield 6 hertz (figures above); 8 poles yield 12 hertz;
– 2𝑛 poles yield 3𝑛 hertz, solving for 𝑛, we obtain 𝑛 = 20. Hoover Dam rotors have 40-poles.
Half-revolutionof rotor completes
1 voltage cycle
Quadrupolar rotor
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❑ More loops on the conducting coil ⇒ Higher voltage.
❑ Rather than putting more loops in a coil, put more coils.
▪ Three phase generator has 3 coils around the rotor.
S N
120 degreeangle
❑ Stator: Cylinder that covers the rotor and includes coils. Stator is static.