Assignment:
1. A simple Rankine cycle coal-fired power plant has given states identified in the following table. The power plant produces 2.1 billion kW-hr/year of electricity. Ignore losses in the pump and turbine. If the generator is 98% efficient and boiler is 84% efficient, and coal costs $30/tonne, determine:
a) The thermal efficiency of the cycle.
b) The total coal energy content required per year.
c) The annual coal expenditures.
d) The mass of CO2 emitted per year from the plant.
e) The mass of CO2 emitted per million kW-hr produced
State Location h (kJ/kg)
1 boiler exit, turbine entrance 2784.3
2 turbine exit, condenser entrance 2041.6
3 condenser exit, pump entrance 340.5
4 pump exit, boiler entrance 346.6
2. The table below provides steady-state operating data for a cogeneration cycle that generates electricity and provides heat for campus buildings. Steam at 1.5 MPa, 280°C, enters a two-stage turbine with a mass flow rate of 1 kg/s. A fraction of the total flow (15%) is extracted between the two stages at 0.2 MPa to provide for building heating, and the remainder expands through the second stage to the condenser pressure of 0.1 bar.
Condensate returns from the campus buildings at 0.1 MPa, 60°C and passes through a trap into the condenser, where it is reunited with the main feedwater flow. Saturated liquid leaves the condenser at 0.1 bar.
a. Sketch this process on a T-s diagram
b. Determine the net power developed, in kW.
c. Determine the rate of heat transfer to the cooling water passing through the condenser, in kW.
d. Determine the overall cycle efficiency.
State P T (C) h (kJ/kg)
1 1.5 MPa 280 2992.7
2 0.2 MPa 2652.9
3 0.1 bar 2280.4
4 0.1 bar 191.83
5 1.5 MPa 193.34
6 0.1 MPa 60 251.13
7 0.1 bar 251.13