FIRST LAW OF THERMODYNAMICSThermodynamicsNote the individual processes the fluid must go through before completing the complete cycle.Rankine cycles will be discussed in greater detail later in this module. Figure 20 shows a typicalsteam plant cycle. Heat is supplied to the steam generator (boiler) where liquid is converted tosteam or vapor. The vapor is then expanded adiabatically in the turbine to produce a workoutput. Vapor leaving the turbine then enters the condenser where heat is removed and the vaporis condensed into the liquid state. The condensation process is the heat-rejection mechanism forthe cycle. Saturated liquid is delivered to the condensate pump and then the feed pump whereits pressure is raised to the saturation pressure corresponding to the steam generator temperature,and the high pressure liquid is delivered to the steam generator where the cycle repeats itself.Figure 20 Typical Steam Plant CycleWith the example complete, it seems appropriate to discuss the various components of a typicalsteam plant system. Although such a system is extremely complex, only the major componentswill be discussed. A typical steam plant system consists of: a heat source to produce the thermalenergy (e.g. nuclear or fossil fuel); a steam generator to change the thermal energy into steamenergy (a complete steam plant usually exists in connection with the steam generator inconverting the steam into eventual electrical energy); pumps to transfer the fluid back to the heatsource (reactor coolant pumps in a nuclear reactor); a pressurizer to ensure that the primarysystem maintains its desired pressure; and the necessary piping to ensure the fluid passes througheach stage of its cyclic process. Of necessity, the steam plant is a large "closed" system.However, each component of the system is thermodynamically analyzed as an open system asthe fluid passes through it. Of primary importance is the process of dissipating the energycreated by the heat source. This process takes place in the steam generator, which acts as a gianttwo-phase heat generator.HT-01 Page 62 Rev. 0
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