Exam 20240116 Eng

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ENERGY CONVERSION Exam 16/01/2024 Please, write your person code and surname-name on all sheets you hand in. Exercise 1 (10 points) A natural gas-fired gas turbine in simple-cycle configuration is employed for producing electricity during on-peak hours. Originally, the cycle was characterized in reference ambient conditions by: • mass flow rate of breathed air: 350 kg/s, • compressor pressure ratio: 22, • total turbine inlet temperature: 1300 °C, • net electric power output: 110 MW. After years of operation, the first expansion stage has been updated with a new thermal barrier coating allowing for a new total turbine inlet temperature of 1400 °C and an increased power output by 12%. The investment of the update will be recovered in 3 years assuming an equivalent operation of 1500 h/year, an electricity price of 250 €/MWh, and a natural gas cost of 30 €/MWh. Neglecting all pressure drops but that in the combustor, please: i. clearly motivate the solution procedure and highlight the assumptions (1 point); ii. sketch the process flow diagram as well as the cycle on the T-s diagram both before and after the update (2 points); iii. determine the original mass flow rate of burnt natural gas and net electric efficiency (2.5 points); iv. estimate the new turbine outlet temperature, new net electric efficiency, and investment cost of the update (3 points); v. elaborate without further calculations whether the investment would be more profitable if the gas turbine were in com- bined cycle configuration (1.5 points). Exercise 2 (12 points) A flow of exhaust combustion gas is used as a hot source for a power production plant. The mass flow rate of exhaust gas is 100 kg/s and it is available at a temperature of 500 °C. Consider two alternative closed gas cycles, both using CO2 as…