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THERMODYNAMICS - CASE STUDY

    Introduction


Schematic of the Cogeneration Power Plant

 

Due to the rapid rise in fuel prices, and the potentially energy efficient of district heating (DH) system, the use of district heat is on the rise in many countries. A new community, that is under construction in Oklahoma is considering this system. A cogeneration vapor power plant in this community is used to provide the district heating as well as generate the electricity for the community.

What is known:

  • Steam enters the turbine at 16 MPa and 600oC
  • Steam is extracted from the turbine at 5 MPa and sent to heat exchangers. Steam leaves the heat exchanger as saturated water, and the heat exchanger has an efficiency of 85%.
  • The total district heating requirement is 1,100 kW in winter.
  • The electricity requirement from this power plant is 5,500 kW in winter.
    Question




 
  • What is the water mass flow rate through the boiler?
  • What is the utilization factor of this cogeneration power plant?
    Approach

   
  • Model the cycle as an ideal cogeneration Rankine cycle.
  • Use the water tables to determine the enthalpy at each state except state 3. The enthalpy at state 3 can be calculated from the energy balance of the mixing chamber.