Exercise 4 Second law analysis of steam rankine cycles

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ENERGY CONVERSION A 2016-17 1 Exercises Second-law analysis of steam Rankine cycles Exercise 1 Considering a water-cooled two-reheat coal-fired USC in Italy, please compute and comment on the wasted work [kJ/kg] caused by the following hypothetical throttling irreversibilities:  inlet to the high pressure turbine: Δp = 10 bar;  regenerative bleeding at 5 bar: Δp = 0.1 bar;  outlet from the low pressure turbine: Δp = 0.01 bar;  inlet of the first preheater: Δp% = 10%.  outlet of the last preheater: Δp = 10%. Exercise 2 Consider adopting alternatively a direct heat exchanger or an indirect heat exchanger to preheat the feedwater from 100 to 120°C. In the former case, saturated steam at 120°C is employed, while in the latter case, saturated steam at 125°C (heat of condensation for both of 2200 kJ/kg). Please: i. compare the wasted work specific to the feedwater mass flow rate [kJ/kg] in the two cases due to the different heat transfer irreversibility, ii. compute the ratio of mass flow rate of bleed steam and of feedwater. Exercise 3 Consider the low-pressure preheating line of a steam power plant characterized by: • gross electric power output: 500 MW; • gross electric efficiency (LHV): 40%; • condensing temperature: 35 °C (enthalpy of condensation at 35 °C = 2420 kJ/kg); • deaerator temperature: 130°C; • deaerator pressure: 2.7 bar (absolute). Please: i. plot the plant layout from the condenser to the deaerator; ii. sketch the TQ diagram of the entire low-pressure preheating line; iii. calculate the second-law efficiency loss due to fluid -dynamic irreversibility in the condensate pump; iv. calculate the second-law efficiency loss due to the heat transfer irreversibility in the first preheater (assume an enthalpy of condensation of about 2300 kJ/kg); Exercise 4…