HW7_Solutions

# HW7_Solutions - DEPARTMENT OF CIVIL AND ENVIRONMENTAL...

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1 DEPARTMENT OF CIVIL AND ENVIRONMENTAL ENGINEERING UNIVERSITY OF CALIFORNIA, BERKELEY CE11 ENGINEERED SYSTEMS AND SUSTAINABILITY, SPRING 2009 H OMEWORK 7: E ND - OF - LIFE O PTIONS , F OSSIL F UELS DUE F RIDAY , A PRIL 10, 2009 (T OTAL : 100 POINTS ) Note: for the problems 1 and 2, you may find the following information useful. Estimates: Energy requirements and CO 2 emissions per kg of aluminum produced from bauxite and from recycled aluminum. Source of aluminum Primary energy (kJ/kg) CO 2 emissions (kg/kg) Bauxite 235,000 13.1 Recycled 5,150 0.48 1. Aluminum Cans Recycling (20 points) Aluminum cans in the 1970s were considerably heavier than they are now. a. For a 0.355-L (12-oz) aluminum can, with mass 0.0205 kg, and using a 25 percent recycling rate, find the primary energy required to produce the aluminum in one such can. (10 points) Heavier cans from the 1970s, 0.0205 kg/can, and 25% recycling rate: - energy for new aluminum per can = 0.75*20.5 g/can*235 kJ/g = 3613 kJ/can - energy for recycled amount per can = 0.25*20.5g/can*5.15 kJ/g = 26.4 kJ/can - total energy per can = 3613 + 26.4 = 3639 kJ/can b. What percent reduction in primary energy has resulted from the lightweighting of cans and the higher recycling rate that have been achieved lately respectively 0.016 kg and 63 percent? (10 points) Applying the same approach, we find that the primary energy for aluminum today is about 1443 kJ/can. Thus, the percent (%) reduction in primary energy = ((3639 kJ/can-1443 kJ/can)/3639 kJ/can)*100 = 60% 2. More on Aluminum Cans Recycling (15 points) In the United States approximately 1.6·10 6 tonnes/year of aluminum is used in beverage cans, 63 percent of which is recovered and recycled. Using the estimates given below, determine the following: a. The total primary energy used to make the aluminum for those cans. (5 points)

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## This note was uploaded on 05/08/2011 for the course CE 11 taught by Professor Horvath during the Spring '11 term at University of California, Berkeley.

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HW7_Solutions - DEPARTMENT OF CIVIL AND ENVIRONMENTAL...

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