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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 metin@utdallas.edu 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

▪ Cycle ∈ {Brayton, Rankine, Allam, Combinations, … }

▪ Single-phase medium cycle

▪ Open vs. closed (Brayton) cycle

▪ Two-phase medium (Rankine) cycle

▪ Combined cycle

▪ 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.

Coal combustion pollutes:

➢ More carbon dioxide emissions than oil and

natural gas per unit of heat.

o Coal has more carbon than oil & gas.

o Other pollutants: Sulfur dioxide, Mercury

Natural Gas Combined Cycle (NGCC) plants

(45-50%) are more efficient than (36-40%)

Supercritical Pulverized Coal (SCPC) plants.

BUT

Natural Gas Combined

Cycle (NGCC) plant

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Pulverized Coal Power Plants

Pulverized Coal: Finely ground coal particles. Pulverization ⇒ Easier combustion.

In: 208 ton/hr

Out: 500 MW

2,445 ton/hr

149 oC

3) 18.2 ton/hr

1) Bottom Ash4.6 ton/hr

163 atm538 oC

2) Lime slurry22.6 ton/hr lime CaO145 ton/hr water

Wet FGD Solids 41 ton/hrFlue Gas Desulfurization

(FGD) to remove Sulfurdioxide

4) Stack Gas 2,770 ton/hr55oC; 1 atmN2 66.6%H20 16.7%CO2 11%O2 4.9%Ar 0.8%

SO2 22ppmNOx 38ppmHg <1ppb

Hg: Mercury

ppm 1 in million

ppb 1 in billion

Subcritical 500 MW Plant without CO2 Capture

Source: p. 116 of

The Future of Coal

by MITEI

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Supercritical Pulverized Coal Power Plants Heat Efficiency ↑ & Emissions ↓

Supercritical Pulverized Coal Plants have higher temperature & pressure in the boiler.

Heat efficiency is energy content in the output divided by content in the input coal.

Subcritical Pulverized Coal Plant: 36.8% < 39.1% : Supercritical Pulverized Coal Plant.

316 atm610oC

In: 164 ton/hr

Out: 500 MW

4) 2,200 ton/hr

32.5 ton/hr

3) 14.4 ton/hr

1) 3.64 ton/hr

2) 17.9 ton/hr

Source: p. 116 of

The Future of Coal by MITEI

Post-Combustion CO2 capture:

Bind/capture the CO2 with fluids.

Cost = $50-100/ton of CO2.

Chemical scrubbing liquids: Mono-ethanol-amine (common), Chilled ammonia, Potassium carbonate. Physical absorption. Membrane separation

Use Carbondioxide in enhanced recovery Carbon Sequestration:Storing carbon in depleted reservoirs/caves

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Subcritical vs. Supercritical PC Power PlantsHeat Rate Comparisons

Heat Rate =input in Btu per hour

output in kWh per hour

▪ Input per hour = 208,000 kg/h in subcritical plants = 5,200 MM Btu/h = 5,200,000,000 Btu/h

Recall 1 kg coal gives about 0.025 MMBtu

▪ Output per hour = 550 MW = 550,000 kW

𝐇𝐞𝐚𝐭 𝐑𝐚𝐭𝐞 =Input

Output=5,200,000,000

550,000= 9,454

Btu

kWh

▪ Physical meaning: It takes 9,454 Btu to generate 1 kWh.

Capacity Efficiency Plant cost Electricity cost Retail price

Subcritical 550 MW 36.8% $852 M 6.40 cents/kWh 10 cents/kWh

Supercritical 550 MW 39.1% $866 M 6.33 cents/kWh 10 cents/kWh

Source: www.netl.doe.gov/energy-analyses/pubs/deskreference/B_PC_SUB_051507.pdf

www.netl.doe.gov/energy-analyses/pubs/deskreference/B_PC_SUP_051507.pdf

➢ 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].

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Transformation: Kinetic → Electrical

▪ Power vs. Energy

▪ Generators

▪ Single-phase bipolar

▪ Frequency of alternating current

▪ Three-phase bipolar

▪ Multi-phase multi-polar

12 kW Pulsar Generator

Gasoline, Propane → Electricity

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Power is height of a bar;

Energy is area under the bar.

Electrical Energy kWh = kW×h

E(?)P(t)

ts

𝐸 [0, 𝑠] = න0

𝑠

𝑃 𝑡 𝑑𝑡

E(?)

P(t)

ts

𝐸 {1, , … , 𝑠} = 𝑃 1 +⋯+ 𝑃 𝑠 × 1

=

𝑡=1

𝑠

𝑃 𝑡

1 2 3 4

P(1)P(2)

P(3)P(4)

P(s)

time in h

power in kW

Constant power

over each interval

Varying power

within each interval

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Electrical Energy ConsumptionHome Appliances

▪ 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.

❑ Polyphase generators have multiple coils.

StatorS

N

S

N

4-phase, 6 polar generator 3-phase, 2 polar generator 6-phase, 6 polar generator

Coil 1

Coil 2 Coil 3

3-p

has

e, 2

-po

lar

gen

erat

or

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Summary

Combustion

Generation

Based on

- Thermodynamic Cycles, Chapter 4 of Energy Resources and Systems by T.K. Ghosh

and M.A. Prelas, Springer 2009.

- Structure, Operation and Management of the Electric Supply Chain, Chapter 2 of

Electricity Markets by C. Harris. Published by Wiley 2006.

- Electric Power Systems by S.W. Blume IEEE Press 2007.

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Some Thermodynamics, Ideally Speaking

▪ Brayton cycle. Single-phase medium: Air

Turbine

Combuster

Cooler

Compressor

Cool at

constant P

Pressure P

Volume V

Heat at

constant P

Compress

𝑃 ⇑ and 𝑉 ↓

Turbine

𝑃 ↓ and 𝑉 ⇑

Kinetic & HeatEnergy

Kinetic & HeatEnergy

▪ Rankine Cycle = Two-phase medium: Water + Steam

Turbine

Combuster

Cooler

Compressor

Kinetic & HeatEnergy

Kinetic & HeatEnergy

Steam in

the pipes

Water in

the pipes

Air in the

pipes

Pressure P

Volume V

Heat at constant P

Compress

𝑃 ⇑ and 𝑉 ↓

Turbine

𝑃 ↓ and 𝑉 ⇑

Cool at constant P

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Which is correct? Electric vs. Electrical

Electric must be used when referring to a device that uses electrical power to operate:

Electric car sales are going up.

Electric guitar gives metalic sound that irritates some people.

Electric blankets can cause electric shocks.

Electric can be used in a metaphoric sense:

The stockholder meeting had an electric atmosphere.

Electric is used in specific contexts while electrical is more appropriate for general

contexts:

GE produces electric bulbs, microwaves, ovens, dryers and makes a substantial amount of its

revenue from selling electrical goods.

When the TXU technician arrived at my house, he asked for the location of electric cables.

When the ATT technician asked for the location of electrical cables in my house, I showed him

the electric cables, phone cables and TV cables.

High definition TV is an electric machine that is designed by electrical engineers.

Electric energy or electrical energy, or both?

When talking about the energy of an electron in an electric field, use electric energy

When talking about the energy generated or delivered by electric current, use electrical energy

Your suggestions for appropriate use?