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Politecnico di Milano Department of Energy - School of Industrial Engineering Course Energy Systems LM prof. E. Martelli, M. Romano - Academic Year 2016/17 Written Exam – Energy systems LM pag. 1 di 1 Written Exam 27-Feb-2017 Time: 1.00 h PLEASE NOTICE 1) Books, lecture notes, cell phones are forbidden. Using them or t alking with colleagues and/or copying will lead to the immediate invalidation of the exam. 2) Answer clearly ONLY to the questions posed by the problem sets. Even if correct, a dditional considerations will NOT be considered. 3) Fill this sheet with your name and return it. 4) Writing and sheet/page sequence must be left to right as used in western countries. FIRST NAME………………………......……FAMILY NAME……………………………….. Question 1 (15 points) A) Write the definition of LHV of a fuel B) Provide the definition of the thermal efficiency of a combustion boiler. C) Briefly discuss the type of losses affecting a boiler and how such losses can be minimized. D) Discuss the effect of air preheating and explain its effect on boiler efficiency and exergy efficiency of the process. Question 2 (15 points) A) Draw the flowsheet of a heat recovery steam cycle with an HRSG with 2 evaporation levels and reheat. Assume that the rehater operates at the same pressure of the low pressure evaporation level. B) Draw the T-Q diagram of the HRSG, indicating reasonable values for the key design temperature differences ∆Ts which are considered for its design. C) Define the first law efficiency, the heat recovery factor and the cycle efficiency. D) Refer now to a single evaporation level HRSG. Discuss the possible control strategies for operating the cycle at part load, i.e. when the flow rate of the hot gas is reduced assuming negligible changes of gas temperature. Discuss in particular…