Energy Engineering - Solar and Biomass Power Generation

Full exam

SOLAR AND BIOMASS POWER GENERATION AY 2021-22 11 th January 2022 Prof. Giampaolo Manzolini Time: 100 minutes Instructions for the examination: 1) Clearly indicate your surname and name on all the sheets 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 expla- nations will not be taken into account. The final score can be normalized according to the average results. 3) Answer briefly and clearly only to the asked questions. Calculations and explanations which do not respond to the questions will not be considered for evaluation even if correct. 4) Talking with colleagues and / or cheating will cause the cancellation of the exam. 5) 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.). 6) Not all the provided inputs are necessary for the problem solving CSP exercise (16 points) Question A (5 points): A CSP plant based on solar tower technology produces 400 GWh of electricity in a year. The solar plant counts 10’000 heliostats by 90 m 2 each and the DNI and diffuse radiations are equal to 2750 kWh/m 2/y and 350 kWh/m 2/y, respectively. Calculate the average efficiency of the different conversion steps (optical, thermal, piping, power block and auxiliaries) knowing that the yearly optical efficiency is equal to 65%, the power block operates always at full load between 550°C and 300°C the second law efficiency is equal to 57%, piping losses can be neglected while the auxiliaries consumptions are 1 MW every hour of the year, regardless the plant is operating or not. For simplicity assume a constant ambient temperature of 30°C. Question B (6 points): Calculate the optical and thermal efficiencies of the solar plant at design conditions knowing that the oper- ating hours of the previous point were 3800 hours, while the design DNI is equal to 925 W/m 2. The solar to electric efficiency at design conditions is equal to 20% Question C (5 points) Determine the power balances, HTF mass flowrates (average heat capacity 1.5 kJ/kgK, density 800 kg/m 3) and the TES volume making your own reasonable assumptions. If you could not calculate the previous point assume a thermal efficiency equal to 80%. Biomass exercise (16 points) Question A (6 points): Design the biogas plant according to the information reported below. The feed is waste from cheese industry and the BMP on COD basis is 0.35 Nm 3/kg COD and assuming a biogas LHV equal to 9.6 kWh/Nm 3. The biogas plant is connected to the tomato industry and the heat cogenerated is supplied to the industry itself (operating hours are reported in the table below) Amount Conversion factor Mass flow rate (AR) 190 t/d Proteins 14 g/100 gVS 1.42 gCOD/gVS Total solid content 13 g TS/100g Carbohydrates 72 g/100 gVS 1.12 gCOD/gVS Volatile solid content 84 g VS/100gTS Lipids 3 g/100 gVS 2.9 gCOD/gVS The actual Biogas Methane Production efficiency (η BMP ) is function of the Hydraulic Retention Time (HRT) according to the following equation: ������������=1− 1 0.3∙������������������������������������������������ ; Calculate the electricity produced and the thermal power cogenerated by the plant HRT >35 Days OLR