ES210719 practical test

Page 1

POWER PRODUCTION FROM RENEWABLE ENERGY AY 2020-21 19th July 2021 Prof. Silva Time: 1.5 hours Instructions for the examination: 1) Clearly indicate your name on all the files you will deliver. 2) The score refers to exercises done in a comprehensive manner with exact numerical results. Numerical results correct but not accompanied by explanations will not be taken into account. The final score can be normalized according to the average results. 3) Talking with colleagues and / or cheating will cause the cancellation of the exam. 4) All the needed data for the resolution of exercises lies on this paper. It is NOT ALLOWED to use material other than this (e.g. books, clipboard etc.). Exercise 1 (16 points) A geothermal source has the following characteristics at the outlet of the well: pressure 7 bar, vapor fraction 85%, mass flowrate 15 kg/s. Draw the power plant lay-out in a configuration with a direct mixing of the 2 liquid flows (without atmospheric vessel) (1 point) and determine the net power output (3 points), considering a con- densing pressure of 0.1 bar and assuming a steam turbine isentropic efficiency of 88% and a generator or- ganic-electric efficiency of 97%. Calculate the net electric efficiency considering a minimum reinjection tem- perature of 40°C and an overall auxiliary consumption of 700 kW (2 points). In order to increase the power output, the geothermal fluid is further heated to 440°C (enthalpy 3353.4 kJ/kg, entropy 7.758 kJ/kgK) in a biomass boiler (series configuration and neglecting pressure drops, biomass is oak described in the table below ). The boiler has an efficiency of 90% and consists of an evaporator , a super- heater and a regenerative air pre-heater fed by the exhaust gases. Determine the overall net electric efficiency…