EnergyConverting Coal to Electricity
CBEE
Agenda
How Does Conversion Occur?
Rankine, Brayton and Combined Cycles
Combined Heat and Power
Emissions and Emissions Controls
Advanced Materials and Sustainable Energy Lab
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Coal
Petroleum
Hydro
Wind
Solar
Direct use of sunlight for building use (illumination, passive solar heating) not included
Advanced Materials and Sustainable Energy Lab
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Bituminous Coal
“soft coal”
Sub-Bituminous coal
(not pictured)
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The conversion chain
As we discuss matters in class we may use the terms “primary energy”, “delivered energy” and “useful energy”
What is the difference?
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Example for discussion
A coal fired power plant burns 300 tons of sub-bituminous coal per hour to yield 620 MWe.
What is the primary energy content?
How much energy was produced?
What is the efficiency of the process?
Advanced Materials and Sustainable Energy Lab
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Example
A) looking at the coal slide that came before we get sub-bituminous coal yields 24 GJ/ton
Therefore 300 tons x 24GJ/ton = 7,200 GJ = 7.2 TJ
B) Taking the 620 MW over an hour, we get
620 MW x 3600s = 2.23 TJ
C) Efficiency is the ratio between the produced power and the primary power
2.23TJ / 7.2TJ = 32.3% efficiency
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Efficiency
1st law of thermodynamics
The increase in the internal energy of a system is equal to the amount of energy added by heating the system minus the amount lost as a result of the work done by the system on its surroundings
(conservation of energy)
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Carnot Efficiency
2nd law
The entropy change of any process is greater than or equal to zero
(i.e., there will always be some wasted energy)
The Carnot Efficiency is the *maximum* efficiency of a heat engine
(i.e., a heat engine can only run less efficiently than that, not more)
Advanced Materials and Sustainable Energy Lab
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From conversion chain:
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Assume grid efficiency ≈ 92%
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From the table and info we can get the following
Advanced Materials and Sustainable Energy Lab
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Major advantages:
Minimizes release of unbunrt fuel in FBC
Advanced Materials and Sustainable Energy Lab
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“Giovanni Branca’s prime mover”
Described in 1629
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Steam Turbines – impulse wheel 1
Think of Branca’s device
Conversion of steam (heat) to motion relies on escaping high pressure gas making a jet
Let’s use 1000 m.s-1 as a reasonable jet speed
Advanced Materials and Sustainable Energy Lab
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Steam Turbines – impulse wheel 2
Conversion of kinetic energy in jet to motion accomplished by collision with paddles
Maximum energy transfer occurs when paddle speed = ½ jet speed
If jet speed = 1000 m.s-1 then paddle speed = 500 m.s-1
Think of small radius device (original Parsons turbine is 15cm)
What is angular velocity for device? (in rpm)
Advanced Materials and Sustainable Energy Lab
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Developed by Charles Parsons, 1889
Basically, a set of vanes converting steam jet speed into motion
Advanced Materials and Sustainable Energy Lab
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Particulate Matter (PM)
bag filters/electrostatic precipitators
CO2: “carbon capture and sequestration”
Much research into Carbon Capture coal power plants
Advanced Materials and Sustainable Energy Lab
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Combined heat and power
Dealing with combustion products
Electric power system primer
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system
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