Environmental Engineering Reference
In-Depth Information
first decade of the twentieth century increasingly as unit
drives. Devine (1983) and Schurr (1984) document the
rapidity of this critical transition in the United States.
While total installed mechanical power in manufacturing
roughly quadrupled between 1899 and 1929, electric
power capacities grew nearly 60-fold, from less than
5% to over 82% of total power. Since then, the share of
electric power has changed little; the substitution was
practically complete in just three decades. Its benefits
translated into superior productive efficiencies, opened
the way for flexible plant design and easy expansion, en-
abled precise machine control and highly focused power
applications, did away with the overhead clutter, noise,
and health risks, freed ceilings for installation of better il-
lumination and ventilation, and resulted in higher labor
and capital productivity (see section 12.2).
Electric motors also revolutionized passenger rail
transport. The latest version of the world's first high-
speed train (700 series), Japan's T
¯
kaid
¯
shinkansen,
which has been in operation since October 1964, draws
electricity from catenary wires (copper or copper-clad
steel) with spans of 50 m as 25 kV AC at 60 Hz, and it
has 64 275-kW AC motors (four in each car) for the to-
tal of 13.2 MW. This makes frequent accelerations and
decelerations, needed for relatively short interstation
runs, easier, and the motors also function as dynamic
brakes once they become generators driven by the wheels
and exert drag on the train. Pneumatic brakes are used
for speeds below 30 km/h and as a backup. The French
TGV, unlike the shinkansen, has two locomotives (power
cars) in every train set, each weighing 68 t and capable of
4.4 MW (TGVweb 2000). Electric supply and subse-
quent conversions are similar to the Japanese practice. A
pantograph picks up AC at 25 kV and 50 Hz, a rectifier
converts it to 1500 V DC, and traction inverters convert
DC to variable frequency AC, which is fed to synchro-
nous motors that are also used for dynamic braking at
high speeds. Both of these trains are capable of speeds of
300 km/h.
But the modern world's great reliance on electricity
has a major drawback: unacceptably high energy loss
during thermal generation, particularly in coal-fired
plants (see section 8.5). Only the best individual stations
have efficiencies of 40%-42%. Co-generation—the use
of a single primary heat source to produce simultane-
ously electricity and heat, saving 10%-30% of fuel in
comparison with a separate generation of the two final
energies—is an old technique, but its rapid commercial
diffusion dates only to the 1970s (Hu 1983; E. L. Clark
1986; Boyce 2002; Petchers 2003). The technique has
made substantial inroads only in Europe and Japan.
9.5 Energy Conservation: Gains and Rebounds
I agree with Rose (1986) that the term rational and ef-
fective energy use is preferable to conservation (the first
law of thermodynamics dictates that energy is always
conserved), but I subsume all approaches to reducing en-
ergy use under that imprecise but widely established
word, used in so many post-1973 publications (Ford
et al. 1975; Lovins 1976; Socolow 1977; Gibbons and
Chandler 1981; Hu 1983; Rose 1986; Casten 1998;
Goldemberg 2000; WEC 2006). Most of the attention
has been given to improving device efficiency (for in-
stance, compact fluorescent lights instead of light bulbs),
but on an individual level such gains can be much
reduced or canceled by inefficient use (leaving the light
on) or lack of system benefits (light may be too far
away). In terms of broad strategies, a trio of basic
