Chemical, Biological and Environmental Engineering Converting Coal to Electricity

Advanced Materials and Sustainable Energy Lab CBEE Agenda Where Does the Energy Come From? How Does Conversion Occur? The Carnot Limit (system efficiency concepts) Rankine, Brayton and Combined Cycles Combined Heat and Power Emissions and Emissions Controls Electric Generators, Transmission and Distribution, Real and Reactive Power

Advanced Materials and Sustainable Energy Lab CBEE “Primary energy” Energy content of original resource Coal Natural gas Petroleum Hydro Wind Solar Direct use of sunlight for building use (illumination, passive solar heating) not included

Advanced Materials and Sustainable Energy Lab CBEE How much reserves in fossil fuels?

Advanced Materials and Sustainable Energy Lab CBEE How much reserves in fossil fuels?

Advanced Materials and Sustainable Energy Lab CBEE How long will that last?

Advanced Materials and Sustainable Energy Lab CBEE What is “Coal” Anthracite “Hard Coal” or “Black Coal” Bituminous Coal “soft coal” Sub-Bituminous coal Also “Lignite” or “Brown Coal” (not pictured)

Advanced Materials and Sustainable Energy Lab CBEE

Advanced Materials and Sustainable Energy Lab CBEE Why the difference

Advanced Materials and Sustainable Energy Lab CBEE 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?

Advanced Materials and Sustainable Energy Lab CBEE Example for discussion A coal fired power plant burns 300 tons of sub- bituminous coal per hour to yield 620 MW e. a)What is the primary energy content? b)How much energy was produced? c)What is the efficiency of the process?

Advanced Materials and Sustainable Energy Lab CBEE 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

Advanced Materials and Sustainable Energy Lab CBEE Efficiency 1 st 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)

Advanced Materials and Sustainable Energy Lab CBEE Carnot Efficiency 2 nd 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 CBEE Efficiency of a series of processes From conversion chain: combustion (& heat exchanger) → steam turbine → electric generator → distribution grid → appliance

Advanced Materials and Sustainable Energy Lab CBEE Example: Efficiency of an incandescent lamp Assume grid efficiency ≈ 92% Already include typical Carnot term

Advanced Materials and Sustainable Energy Lab CBEE Example: Efficiency of an incandescent lamp From the table and info we can get the following

Advanced Materials and Sustainable Energy Lab CBEE Prevalent Combustion Systems

Advanced Materials and Sustainable Energy Lab CBEE Pressurized Circulating Fluidized Bed Combustor Major advantages: Keeps heat exchanger out of the combustion zone Minimizes release of unbunrt fuel in FBC

Advanced Materials and Sustainable Energy Lab CBEE

Advanced Materials and Sustainable Energy Lab CBEE Converting heat to motion “Hero’s Machine” (aeolipyle) Described by Ctesibius in 250 BC “Giovanni Branca’s prime mover” Described in 1629 Followed by Savery, Newcomen, Watt and Trevithick

Advanced Materials and Sustainable Energy Lab CBEE 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 CBEE 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 CBEE Reaction turbine Developed by Charles Parsons, 1889 Basically, a set of vanes converting steam jet speed into motion

Advanced Materials and Sustainable Energy Lab CBEE

Advanced Materials and Sustainable Energy Lab CBEE Steam turbines

Advanced Materials and Sustainable Energy Lab CBEE

Advanced Materials and Sustainable Energy Lab CBEE

Advanced Materials and Sustainable Energy Lab CBEE Combustion Emissions SOx –de-SOx slurry injection NOx –de-NOx ammonia/urea injection, selective catalytic reduction Particulate Matter (PM) –bag filters/electrostatic precipitators CO / CO 2 –CO usually not an issue with well-controlled power plants –CO 2 : “carbon capture and sequestration” –Much research into Carbon Capture coal power plants

Advanced Materials and Sustainable Energy Lab CBEE Looking Ahead Next week: –Brief intro/review of thermo –Rankine, Brayton and Combined Cycles –Combined heat and power –Dealing with combustion products – Electric power system primer

Advanced Materials and Sustainable Energy Lab CBEE Electric Grid