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THERMODYNAMICS - CASE STUDY

    Introduction


Problem Description
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When Mike attended an on-site interview by an energy company for a summer job in a steam power plant, an engineer showed him where a Rankine cycle running. The engineer then gave him some basic data and asked him to figure out the steam fraction extracted from the turbines and the thermal efficiency of this cycle.

What is known:

  • Steam enters the first turbine at 16.0 MPa and 600oC.
  • The pressure in the condenser is 10.0 kPa.
  • While some steam is extracted from the high-pressure turbine at 5 MPa and sent to the closed feedwater heater, the remaining steam is reheated to 600oC. The extracted steam is condensed as saturated liquid at 5.0 MPa and trapped to the open feedwater heater.
  • Some steam is extracted from the lower-pressure turbine at 1.0 MPa and sent to the open feedwater heater.
    Question




 
  • Determine the steam fraction extracted from the turbines.
  • Determine the thermal efficiency of this cycle.
    Approach



 
  • The steam power plant operates on an ideal reheat-regenerative Rankine cycle with one open feedwater heater, one closed feedwater heater, and one reheater, as shown in the diagram.
  • Use the water tables to determine the enthalpy at each state.
  • The fractions of steam extracted are determined from the mass and energy balances of the feedwater heaters.

Schematic of the Power Plant and its T-s Diagram for the Complete Cycle