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ENERGY CONVERSION A 2017-18 Name/Lastname:__________________________________________ Code n.___________ Exam 23/01/2018 Exercise 1 (10 points) Consider a mid-size coal-fired subcritical steam Rankine cycle characterized at nominal conditions by:  net electric power: 250 MW,  pressure of the steam to the high-pressure turbine: 180 bar,  temperature of the steam to the high-temperature turbine: 560°C;  mass flow rate of the steam to the high-pressure turbine: 1080 t/h. The power output is governed by a throttling valve at the inlet of the high-pressure steam turbine. During a partial load operation, pressure at the inlet of the high-pressure turbine is reduced by 15%. Please: i. motivate clearly the solution procedure and highlight neatly the assumptions (1 point); ii. sketch carefully the overall plant layout and the cycle at nominal conditions on the T-s diagram (2 points); iii. stating the simplifying assumptions, compute the mass flow rate to the high-pressure turbine at that partial load (3 points); iv. assuming constant pressure at the valve inlet, calculate the permanently wasted power due to throttling at that partial load (2 points); v. suggest and describe a better way of controlling the power output (2 points). Exercise 2 (12 points) A chemical process employs a gaseous methane stream (Tcrit= ̶ 83°C; pcrit=46 bar, cp0=2.1 kJ/kgK) at 10 kg/s and ambient conditions. For practical reasons, the methane is stored in tanks as saturated vapor at -140°C and then heated. Please: i. motivate clearly the solution procedure and highlight neatly the assumptions (1 point); ii. compute the maximum obtainable power from the methane stream from the tank to the process (2 points); iii. considering a Carnot cycle operating between the ambient and the methane stream,…