Energy Engineering - Solar and Biomass Power Generation

Full exam

SOLAR AND BIOMASS POWER PRODUCTION AY 2019-20 16 th June 2020 Prof. Giampaolo Manzolini Time: 2 hours Instructions for the examination: 1) Clearly indicate your 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 accompa- nied by explanations 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 Exercise 1 (16 points) Consider a biogas plant consisting of a digester with the characteristics of the feedstock reported below. Question a) determine the size of the digester considering a minimum HRT of 23 days and a maximum OLR of 3.5 kg COD /m 3/day the design constraint reported (5 points) Assuming that the actual Biogas Methane Production efficiency (η BMP ) is function of the Hydraulic Retention Time (HRT) according to the following equation: ������������=1− 1 0.33∙������������������������������������������������ ; Question b) calculate the electricity production on yearly base and the resulting LCOE knowing that the supply of the feed is constant throughout the year and the economic assumptions are reported in the table below (4 points) Feedstock cost 5 €/t Power Block cost 1200 €/kWel Digester cost 600 €/m 3 Indirect and contingency cost 50% of total installed cost Operation and maintenance cost 4% of total cost Internal combustion engine electric efficiency 42% Internal combustion engine thermal efficiency 44% Average Thermal Power for digester 200 kW Revenue from Thermal energy sold 20 €/MW h ICE operating hours 8400 h Operating Hours of Thermal energy sold 2000 hours Plant lifetime 20 years Consider that during the third year of operation, the biogas plant has to decide whether continuing with the supply of the same feedstock of the previous point, at the same cost, but reduced to 175 m 3/d or changing the feedstock with another one with 75 g COD /kg biomass and availability of 210 m 3/d with a price of 4 €/t Question c) please indicate the best option demonstrating it with the numbers (7 points) Amount Conversion factor Volumetric flow rate 200 m 3/d Proteins 20 g/100 gVS 1.42 gCOD/gVS Total solid content 14 g TS/100g Carbohydrates 52 g/100 gVS 1.12 gCOD/gVS Volatile solid content 80 g VS/100gTS Lipids 4 g/100 gVS 2.9 gCOD/gVS Exercise 2 (16 points) Consider a CSP plant based on Linear Fresnel technology. The characteristics of the solar field are reported in the following table. (CR concentration ratio) Number of mirrors 60 Mirror width 25 cm Mirror lenght 100 m optical efficiency 0.52 thermal efficiency 1-12/CR DNI 950 W/m 2 Absorber diameter 0.1 cm Question a) Please determine the mass flowrate of the molten salts heated in the receiver knowing that the inlet and outlet temperatures are equal to 290°C and 550°C and the molten salts have an average cp equal to 1.5 kJ/kgK (4 points) Considering that the CSP plant consists of 150 Linear Fresnel collectors of the characteristics above reported and adopts a steam cycle for converting the thermal energy into electricity. Question b) calculate the net power output and conversion efficiency of the plant considering a SM equal to 2 and a second law efficiency equal to 0.55, and the auxiliary consumptions count for 1 MW (4 points) Question c) calculate the volume of the TES assuming that it is sized for 7 equivalent hours and the density is equal to 1.7 t/m 3 (3 points) Question d) Calculate the average tilt angle of the mirrors and the average horizontal distance from the re- ceiver projection on the ground, knowing the characteristics properties of the system below reported. Neglect blocking and shading losses and assume that all the radiation points the secondary reflector and then is di- verted to the absorber (5 points) Mirror reflectivity 0.94 Secondary mirror reflectivity 1 Glass envelope transmissivity 0.95 Absorber absorptivity 0.95 Secondary reflector Intercept factor 0.97 height of the receiver 5 m