Exam 2020 09 04 Solutions

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Department of Energy Politecnico di Milano Author E. Colombo Pag.1 of 12 Date 23/09/2020 Milan, 1st September 2020 Exam – Advanced Thermodynamic and Thermoeconomics Session of 04-09-2020 Total score: 21 points (exercise 1 roughly 2/3 of the total) Exercise 1. Consider the closed cycle power plant depicted in the figure with a boiler, a turbine, a condenser and a pump. The boiler is fed by fuel & air and it produces steam which enter s the turbine. The turbine produces power for the national electric grid. In the condenser, water condenses by using an external stream of cooling water. The pump closes the cycle and allows the water to enter again the boiler. The pump requirements are 42 MW from the national grid, paid at a cost of 40 €/MWh . The water-steam closed cycle has constant mass flow rate of 1.711 ton/s. Flue gases (cp=1.28kJ/kg K; MM=28.26 kg/kmol) are released to the environment without any additional costs. Cooling water is withdrawn from the environment at zero cost. Stream 6 is not used but recollected in an artificial basin at zero additional costs, ready for other cooling-down purposes. The mass flow rate of Fuel is 0.137 ton/s and its LHV is 49000 MJ/ton, flue gases mass flow rate is instead 5.060 ton/s. The net power of the steam turbine is 2 GW. Thermodynamic data, Physical data and Economic data are given in the tables below. Reference conditions: T0=15°C, P0=1.013 bar. Reference environment: 0.74 N 2, 0.22 O 2, 0.01 CO 2 , 0.03 H2O Flue gases Fuel & Air Cooling water 7 8 Stream T P h s Ex [⁰C] [bar] [kJ/kg] [kJ/ kgK] [MW] 1 700.0 150 3839.48 6.96 3142 2 60.1 0.2 2608.95 7.91 568 3 60.1 0.2 251.40 0.83 23 4 63.0 150 276.17 0.86 51 5 15.0 1.013 63.08 0.22 0 6 35.0 1.013 146.73 0.51 135 7 – Fuel & air ? 8 – Flue gases 90.0 1.013 ? unit cost of Fuel,Air…