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9. Compare the use of paper towels and an air dryer to drying the hands.
Compare environmentally the use of paper towels for drying hands and the
use of a hand-dryer supplied with electricity from a gas thermal power plant
or from an eolic power plant. The considered comparison parameters are
the emissions of carbon dioxide, CO , and sulfur dioxide, SO . Suppose
2
2
that the weight of a paper towel is 7 g and that the electric hand-dryer is
2000 W and works for 30 s. With these data, determine the best way, from
an environmental point of view, to dry the hands. The ELs related to the
paper and the use of electricity are assumed to be the following:
Electricity gas Electricity eolic
Paper thermal power plant power plant
EL Units EL/kg EL/kWh EL/kWh
Lignite kg 1.10 × 10 –1 1.21 × 10 –3 1.68 × 10 –3
Coal kg 1.51 × 10 –1 7.06 × 10 –2 1.10 × 10 –2
Natural gas Nm 3 7.97 × 10 –2 2.09 × 10 –1 2.25 × 10 –3
Crude oil t 1.84 × 10 –4 2.35 × 10 –6 4.82 × 10 –6
Water kg 2.60 × 10 3 3.40 5.15 × 10 1
CO 2 (air) kg 1.46 1.42 3.3 × 10 –2
SO x (air) kg 1.04 × 10 –2 2.07 × 10 –4 1.37 × 10 –4
NO x (air) kg 3.03 × 10 –3 2.16 × 10 –3 7.1 × 10 –5
CH 4 (air) kg 2.04 × 10 –3 1.99 × 10 –3 1.1 × 10 –4
HCl (air) kg 1.30 × 10 –4 1.00 × 10 –6 5.8 × 10 –6
–2
Electricity consumption: Ec (kWh); Ec = (2000 (J/s)/1000); (30/3600) = 1.67 × 10 kWh.

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