Electric Cogeneration facilities where power is produced and what had formerly

Electric cogeneration facilities where power is

This preview shows page 14 - 17 out of 876 pages.

Electric • Cogeneration facilities where power is produced and what had formerly been waste heat is used for heating or cooling. Our current energy consumption patterns, and energy conservation policies that industrialized societies may follow in the future with the resultant chal- lenges for engineers. The Steam Power Plant The first law of thermodynamics states that energy is conserved; it can change form, but it cannot be destroyed. This very simple, fundamental statement allows us to investigate the behavior of many devices and systems (combinations of devices). One of these is the steam power plant, an energy system that is essential to the industrial- ized world, as it often is used for the generation of electric power. Figure 1.1 depicts a simplified steam power plant. Fuel is burned to release heat in a steam generator, similar in concept to the oil- or gas-fired boilers used to provide steam or hot water for heating in homes. The process transforms the fuel's chemical energy to the thermal energy of combustion gases. The heat is used to boil water under pressure in the steam generator (boiler). The steam leaves the generator and passes through superheater tubes, where more heat is added to the steam; it then passes through the turbine, where it increases in volume, decreases in pressure, and performs work by causing the turbine rotor to rotate. The turbine is coupled to a generator, which is used to generate electric power. Thus, in the turbine another process transforms some of the
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Spark plug Throttle Fuel supply -.j- Air supply Carburetor Intake manifold Intake valve Camshaft -o-+--J.;;; l \ I f//'0.\ ~-/ Crankcase " Crankshaft~--~-"~ Oil pan Figure 1.2 A reciprocating internal combustion engine. CHAPTER 1 / INTRODUCTION 3 Rocker ann To atmosphere Combustion chamber thermal energy of the steam into mechanical work. The steam is then condensed, liquefied, and pumped back to the steam generator. The second law of thermody- namics tells us how much thermal energy can be converted into work. Not all of it can be. To fully understand a steam power plant requires knowledge of substance prop- erties: why water behaves as it does, why combustion occurs, what are the combus- tion products, what is the mechanism of energy transformation. Thermodynamics allows us to determine these properties, experimentally and theoretically. Internal Combustion Engines Another standard power plant that many of us use every day is the internal combus- tion engine used to power automobiles and many other machines (Figure 1.2). The
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CHAPTER 1 / INTRODUCTION Chemical energy Fuel is supplied to engine. ~ ~ Thermal energy Combustion raises gas temperature and pressure. ~ ~ Mechanical energy Piston moves because of the high pressure. ~ ~ Shaft energy Crankshaft rotates after translating piston motion.
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