Energy systems LM 17 01 2023

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Politecnico di Milano School of Industrial Engineering Course Energy Systems proff. S. Consonni, E. Martelli, M. Romano - Academic Year 2022-23 Energy Systems LM – written test of 17 January 2023 page 1 of 3 Written Exam of 17 January 2023 - Problems - Time: 2 hours PLEASE NOTICE 1) Exam is open book, but computers and cell phones are NOT allowed. Talking with colleagues and/or copying will lead to the immediate cancellation of the exam. 2) Answer clearly ONLY to the questions posed by the problem sets. Even if correct, additional considerations and/or calculations will NOT be considered. 3) Fill this sheet with your name and return it together with your solutions. 4) Mark each sheet of the solution with your name and page number. 5) In addition to the points obtained for the solution of each problem, a bonus of max 1 point may be given based on whether the solution of each problem is complete, with clear details and explanations. Problem 1 (15 points) A boiler generates 20 kg/s of saturated steam at 15 bar. The boiler features the following parameters: - The boiler consists of a combustor, a heat exchanger (flue gas – steam), an air preheater, a stack - The temperature of the flue gases at the stack is 120 °C - The ambient air temperature is 10 °C - Air composition = 21% O2, 79% N2 - Molar mass of air = 28.84 kg/kmol - The feedwater entering the boiler is at 100 °C, 20 bar - The effectiveness of the air preheater is 80% - The percentage excess of air is 30% - Fuel is pure butane (C4H10: molar mass=58 kg/kmol; LHV=45.75 MJ/kg) - The specific heat capacity at constant pressure cp of the air is 1.02 kJ/(kg K) - The specific heat capacity at constant pressure cp of the flue gas is 1.10 kJ/(kg K) - Heat losses from the combustor walls = 1 % of the LHV - Energy losses due…