Exam 20230711 Eng

Page 1

ENERGY CONVERSION Exam 11/07/2023 Please, write your person code and surname-name on all sheets you hand in. Exercise 1 (10 points) Consider an intercooled gas turbine characterized at 15 °C and 1 bar, named “base case”, by: • overall compression ratio, 𝛽𝑇𝑂𝑇: 42, • low-pressure compression ratio: 𝛽𝐿𝑃 = √𝛽𝑇𝑂𝑇 3 , • high-pressure compressor inlet temperature: 30 °C, • net electric power: 110 MW, • net electric specific work: 520 kJ/kg, • net electric efficiency: 45%; • all air bleedings are from the high-pressure compressor. Moreover, consider an off-design condition, named “better-intercooling case”, in which the high-pressure compressor inlet temperature is 20 °C, without modifying the equipment, in particular the turbomachinery . Neglecting pressure drops, please: i. clearly motivate the solution procedure and highlight the assumptions (1 point); ii. sketch the process flow diagram, the T-s diagram, and the T-Q diagram of the intercooler for the base case (2.0 point); iii. calculate the second-law efficiency loss due to intercooling in the base case (1.5 points); iv. determine the low-pressure compressor technical power in the base case and in the better-intercooling case (3 pts); v. indicate without computing how and why the high-pressure compressor technical power changes from the base case to the better-intercooling case (2.5 points). Exercise 2 (12 points) A liquefied natural gas regasification process is designed as follows. • Methane (critical temperature of -82.6 °C, critical pressure 4.6 MPa, ideal gas specific heat at constant pressure 2100 J/(kg K), and ideal liquid density 420 kg/m3) is stored at ambient pressure in saturated liquid conditions (-161 °C). It is pumped to 8 bar and, then, heated up to -60 °C through heat transfer in a CO2 condenser. The CO2…