a) Calculate the emissions (lb m ) and energy consumption (Btu) per 2000 paper s
ID: 1561778 • Letter: A
Question
a) Calculate the emissions (lbm) and energy consumption (Btu) per 2000 paper sacks used and per 4000 plastic sacks used, assuming that no sacks are recycled.
b) Calculate the emissions (lbm) and energy consumption (Btu) per 2000 paper sacks used and per 4000 plastic sacks used assuming that 70.0% of the sacks are recycled.
By what percentages are emissions and energy consumption reduced for each sack material as a consequence of recycling?
c) If the average use of plastic grocery sacks per day per person in the United States (population 320 x 106) is 1, calculate the average rate of energy consumption (megawatts, MW) associated with the production, use, and disposal of these sacks, assuming that none are recycled.
How many MW would be saved by 70.0% recycling?
Explanation / Answer
a] The total emission and energy consumed will be addition of both the stages i.e. raw materials production plus product disposal + sack production and use.
Hence, emissions per 2000 paper sacks = 2000* (0.0510 + 0.0516) = 2000 * 0.1026 = 205.2lbm.
Emissions per 4000 plastic sacks = 4000*(0.0045 + 0.0146) = 4000 * 0.0191 = 76.4lbm.
Energy consumed per 2000 paper sacks = 2000 * (724+905) = 2000* 1629 = 3258000 Btu.
Energy consumed per 4000 plastic sacks = 4000 (185 + 464) = 4000 * 649 = 2596000 Btu.
b] 70% of 2000 paper sacks i.e. 1400 paper sacks are recycled, so the recycled sacks will not have the contribution from the first stage (raw material production plus product disposal). Hence,
the emission of 2000 paper sacks = 1400 * 0.0516 + 600 * 0.1026 = 133.8lbm.
Similarly, 70% of 4000 plastic sacks counts to 2800 sacks, and the
emission due to th total 4000 plastic sacks = 2800 * 0.0146 + 1200 * 0.0191 = 63.8lbm.
Energy consumed by 2000 paper sacks = 1400 * 905 + 600 * 1629 = 2244400 Btu.
Energy consumed by 4000 plastic sacks = 2800 * 464 + 1200 * 649 = 2078000 Btu.
Due to recycling, emissions and energy consumption is reduced by 34.8% and 31.1% respectively for paper sacks, while for plastic sacks it is reduced by 16.49% and 19.95% respectively.
c] Total number of plastic sacks used in the US = 320 * 106 = 33920.
Hence, the energy consumption for these plastic sacks is = 33920 * 649 = 22014080Btu/day = 917253.33/hr = 0.268640569MW.
Since, 1MW = 3414425.94972Btu/hr.
If 70% plastic sacks are recycled, energy consumption will be = 23744 × 464 + 10176×649 = 17621440Btu/day = 734226.67/hr = 0.215036636MW.
Hence, if 70% plastic sacks are recycled 0.053603933MW or 19.95% energy can be saved.
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