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Question: 1 evaluate the production of ethanol from sugarcane as done...

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1. Evaluate the production of ethanol from sugarcane as done in Brazil. The diagram below shows energy flows (dotted lines) and mass flows (solid lines) throughout the production. Energy in the form of seed, fertilizer, labor and machinery are input to the farm at the left (ha - hectare, a unit of area). 80 Mg of sugarcane per hectare is harvested and taken to an ethanol plant, where it is crushed and separated. The bagasse (woody refuse) is burned, releasing 64.7 MJ/Mg of energy after conversion to electricity. This energy is used to power the rest of the plant, which ferments sugars to ethanol and then distills to produce high purity ethanol. The ethanol is transported to end users (requiring 0.44 GJ per m3 transported), where it is consumed at a higher heating value of 29.7 MJ/kg losses 0.44 CO2, H20 80 Ma transportation 80 to market 36 64.7 sugarcane farm bio-ethanol plant electric grid Perform the following calculations on a basis of 1 hectare of land. a) Given that the plant requires 45.4 MJ of energy for processing and distillation of 1 Mg of sugarcane, does the plant supply energy to the grid or must it purchase electricity? How much? b) How many liters of ethanol are produced? What is the energy content of this final output stream? c) Adding up the input and output (disregarding input from the sun and losses in harvesting and at the plant), what is the ratio of the energy output to the energy input? d) Now consider the input from the sun. If the annual average sunshine in Brazil is about 220 W/m, what is the overall energy conversion efficiency of the process? (Note: the energy cost of farming and productivity of the farm should be considered to be per year.)

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