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Politecnico di Milano Department of Energy School of Industrial and Information Engineering Course Energy Systems LM proff. S. CONSONNI, E. MARTELLI, M. ROMANO - Academic Year 2018/19 Energy Systems LM - test of 20 Nov. 2019 page 1 of 2 Written Exam of 20 Nov. 2019 - 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 3 points may be given based on whether the solution of each problem is complete, with clear details and explanations. FIRST NAME………………………......……..…FAMILY NAME………….………………………….. Problem 1 (16 points) A natural gas firing boiler produces 10 kg/s of saturated steam at 10 bar for a refinery. The plant features the following configuration and working parameters: ‐ The boiler is endowed with a combustor, a flue gas‐steam heat exchanger, an air preheater, a stack ‐ The temperature of the flue gas at the stack is 100 °C ‐ The ambient air temperature is 15°C ‐ The feed‐water is at 15°C, 13 bar ‐ The temperature of the flue gas at the inlet of the air preheater is 200 °C ‐ The combustion is characterized by a 20% excess air ‐ The fuel is pure methane (CH4: molar mass=16 kg/kmol; LHV=50.01 MJ/kg) ‐ Specific heat capacity at constant pressure cP of the air is 1.02 kJ/(kg K) ‐ Specific heat capacity at constant pressure cP of the flue gas is…