Energy Systems LM

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Raccolta di appunti presi durante le lezioni del Professore e sulla base delle sue slides basati su appunti personali del publisher presi alle lezioni del prof. Romano …

Esame Sistemi energetici

Facoltà Ingegneria industriale

Dal corso del Prof. Romano Matteo

Università Politecnico di Milano

A.A. 2016-2017

78 pagine

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Politecnico di Milano - Department of Energy

School of Industrial and Information Engineering

Course: Energy Systems LM

Professors: S. Consonni, E. Martelli, M. Romano
Academic Year: 2015/16
Written Exam: 08 February 2016 - Problems
Time: 2 hours

Please Notice

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.
Answer clearly ONLY to the questions posed by the problem sets. Even if correct, additional considerations and/or calculations will NOT be considered.
Fill this sheet with your name and return it together with your solutions.
Mark each sheet of the solution with your name and page number.
The final grade is the sum of the points assigned to the solution of each problem plus a bonus of max 3 points. The bonus will 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-fired boiler with combustion power 10 MW is fed with natural gas with the following molar composition:

Methane (molecular mass 16 kg/kmol, LHV 50 MJ/kg): 88%
Ethane (molecular mass 30 kg/kmol, LHV 47.8 MJ/kg): 8%
Nitrogen (molecular mass 28 kg/kmol, LHV 0 MJ/kg): 4%

For the sake of simplicity, combustion air can be assumed a mixture of just nitrogen and oxygen, with a molar ratio 3.76.

Questions

Evaluate the mass flow rate of natural gas

At design conditions: both air and natural gas are fed to the boiler at the reference temperature of 25°C; combustion efficiency is 99.5% (i.e., unburned fuel losses = 0.5%); heat losses from the boiler walls are negligible; percentage excess air is 20%; temperature of combustion products discharged by the boiler is 110°C; the boiler generates pressurized water at 10 bar, 140°C; feedwater enters the boiler at 10 bar, 50°C.

Evaluate the oxygen content in dry, combustion products
Evaluate the boiler efficiency
Evaluate the mass flow rate of water heated up by the boiler
Assuming that the combustor is adiabatic, determine the effectiveness of the heat exchanger that transfers heat from the combustion products to the pressurized water
Calculate CO₂ specific emissions [grams of CO₂ per MJ of useful heat]

Combustion power = [fuel mass flow rate]*LHV

Energy Systems LM - written test of Feb 8th, 2016

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