L05 - Chapter 5 Fossil-fuel Electric Power Plants...

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Chapter 5: Fossil-fuel Electric Power Plants – Motivation • Production of energy comes with many undesirable by-products; in this chapter we’ll take a look at the by-products associated with the fossil-fuel plants • A power plant (be it coal, nuclear or hydroelectric) will process the different initial input of energy in the same way: heat is produced and used to boil water and produced steam , which is injected into a turbine to spin an electric generator; the steam is then condensed back into water • In a fossil fuel plant, the heat is obtained by burning coal pulverized in a powder which contains unburnable ash and sulfur which subsequently combines with 5.1 oxygen into gaseous sulfur oxides • Besides the energy content of the coal, the performance of the power plant will also be determined by these unburnable byproducts
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Energy and Emission Model – Conversion steps • Let’s follow the transformations of the energy content in 1000 pounds of coal, with a content of energy of 13000 Btu/lb, as it is introduced in the coal power plant. • We’ll assume some typical efficiencies e for each part of the processing chain: 5.2 Boiler Turbine Generator 88% 47% 99% Smokestack: 1.56 million Btu ~ 50 lb sulfur oxide → 5 lb after filter ~2600 lb carbon dioxide → all into atmosphere ~100 lb ash → 1 lb after filter in use div E E E = + 100 use in E e E = × e = 88% e = 47% e = 99% In Out 13 million Btu 11.44 million Btu 5.377 million Btu 5.323 million Btu = 1560 kWh Condenser 6.063 million Btu
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Coping with Particulate Matter – What is this? • Most solid matter (such as ash) leaves the smokestacks of the power plants in the form of fine particles called particulate matter • For simplicity, particulates are assumed to be spherical and with a diameter that can be inferred by using the concept of mass density ρ (rho) – a quantity describing how much mass m in concentrated in a volume V : • Hence, the particulates are characterized by length (diameter) 5.3 m V ρ = 3 kg m Ex : A spherical particle with a mass of one millionth of a gram (10 –6 g or micro gram μg) and density of 1g/cm 3 = 1000 kg/m 3 has a diameter of about 0.012 cm, as given by The typical size of a particulate is between less than one 0.1 μm and 0.05 cm ( ) ( ) 6 3 6 3 3 3 1 6 6 10 g 6 ~ 2 10 cm ~ 0.012 cm 1 g cm m m m D D V D π πρ = = = = × • The concentration of particulates in the atmosphere is given by their density in one meter cube of air • A certain concentration of particulates includes particles of various sizes, in general in the same proportion everywhere Ex : Typical concentrations range from 10 μg/m 3 in clean areas to 2000 μg/m 3 in polluted areas
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Coping with Particulate Matter – Origins and Damaging Potential • In the US, more than 1400 stations are monitoring the particulates in the air 5.3 • Most mass is in large particulates but most particulates are small (the most damaging for people) • Environmental concerns
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L05 - Chapter 5 Fossil-fuel Electric Power Plants...

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