Lecture 3 - EnergyBalancesandEfficiencyin aPowerPlant

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Energy Balances and Efficiency in a Power Plant What limits the efficient conversion of fossil fuels?
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Energy Conversions Sources
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Efficiency of Energy Conversion Conversion Energies Efficiency Electricity Generators Mechanical Æ Electrical 98-99% Furnaces, Boilers Chemical Æ Thermal 90-98% Electric Motors Electrical Æ Mechanical 90-97% (large) 60-75% (small) Lead-acid batteries Chemical Æ Electrical 85-95% Steam Turbine Thermal Æ Mechanical 40-45% Diesel Engines Chemical Æ Mechanical 30-35% IC Engines Chemical Æ Mechanical 15-25% Fluorescent lights Electrical Æ Radiant 10-12% Incandescent lights Electrical Æ Radiant 2-5% Photovoltaic cells Radiant Æ Electrical 5-20% Photosynthesis Radiant Æ Chemical 0.2-1%
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Coal Fired Power Plant http://www.tva.gov/power/coalart.htm
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Power Plant Process Flow Diagram Furnace Boiler Turbine Condenser Pump Coal Air @ T0 CO2 & N2 @ T1 work water @ T2,P2 water @ T6,P1 steam @ T3,P3 steam @ T4,P4 water @ T0 water @ T5
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Thermodynamics Thermodynamics is the science of energy conversion. It puts different forms of energy on the same scale to assess the feasibility of energy conversion processes.
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Key Elements of Thermodynamics Energy is conserved Watt demonstrated that when energy is converted from one form to another energy must be conserved. Energy always flows down hill Energy always goes from high availability to lower availability. Heat will only go from high temperature to low temperature Cold Hot
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Laws of Thermodynamics 1.You can’t win (it is a zero sum game!) 2. In the long run you lose (the house takes a cut) 3. You have to play the game (it is an essential part of life).
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Mass and Energy Balance on Furnace/Boiler 2 22 2 2 , Moles of Carbon in as coal = Moles of carbon out as CO M Moles of oxygen in with air = Moles of CO out from furnace M Moles of nitrogen in with air = Moles of nitrogen out from f coal CO Oa i r C O M M = = ±± , urnace M Na i r N M = {} { } () 2 2 ,1 0 , 2 10 ,3 Energy carried out Energy from = + Chemic Energy carried ou as ste t in exhaust g al a Reaction a s M
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This note was uploaded on 09/22/2008 for the course MAE 228 taught by Professor Yiguangju,jayb.benziger,roberth.socolow during the Fall '08 term at Princeton.

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Lecture 3 - EnergyBalancesandEfficiencyin aPowerPlant

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