Environmental Engineering Reference
In-Depth Information
Winebrake et al., 2005; Farrell et al., 2002; Quandt, 1996, MAN B&W Diesel, 1997;
Cooper, 2001; Wartsila NSD, 1994). Emissions controls have been categorized as either
pre-combustion, in-engine, or post-combustion controls (Corbett and Fischbeck, 2002).
Technologies that reduce NO
x
emissions can be divided into three groups: those that
require engine modi
cations (in-engine controls), those that are implemented in the fuel
or air system (pre-engine technologies), and those that are on the exhaust system (post-
engine technologies). An important consideration identi
fi
ed in reducing air quality pol-
lutants through technologies and alternative fuels is that nearly all increase the energy
requirements on a system basis by 1-5%, thereby increasing CO
2
emissions attributed to
shipping proportionally.
Fewer studies have considered directly how to mitigate CO
2
emissions; the IMO study
of greenhouse gases from ships presented a suite of alternatives for both new and exist-
ing vessels (Skjølsvik et al., 2000). The IMO study estimated that new vessel CO
2
emis-
sions could be reduced by 5-20% through technological measures, with hull and propeller
modi
fi
fi
cations and engine optimization for e
ciency (rather than power) o
ff
ering the
greatest potential. Other new-engine technologies o
ered only modes CO
2
reductions
(0.5-5%), although a hypothetical combination of technological measures to could
achieve a maximum range of 5-30% reduction. The IMO study estimated that reducing
CO
2
from existing vessels (e.g. through retro
ff
t technologies) would be more challenging,
with reductions from individual measures ranging from 1 to 7%. Some reasonable com-
binations put CO
2
reductions in a range of 5-12%, with a hypothetical combination of all
technological measures at 5-20%.
Alternative marine fuels (other than for performance improvement or cost reduction)
were
fi
rst studied following the 1970s reaction to the energy crisis (National Research
Council, 1980). The possibility of alternative fuels in ocean shipping is receiving renewed
attention, based primarily on environmental concerns about climate change and air
quality (Intertanko, 2006; Wang and Corbett, 2007). Alternative fuels choices should not
be made only on the basis of operating ship fuel consumption, but should also add
impacts of extracting, re
fi
ning and delivering new fuels to replace marine heavy fuel oil
(residual fuel). Assessing complete emissions from marine transportation (and to
compare these emissions with landside alternatives), a total fuel life-cycle emissions analy-
sis is needed (Winebrake et al., 2007a; 2007b; Winebrake et al., 2006). These analyses con-
sider emissions and energy use along the entire fuel pathway - from extraction to use. In
any case, the freight sector overall, and perhaps oceangoing shipping in particular, may
o
fi
er some advantages in a shift to alternate transportation fuels (Farrell et al., 2003).
More directly, environmental mitigation through behavior change is also an option
(Kågeson and Nature Associates, 1999; Theis et al., 2004). Operational measures, pri-
marily
ff
er greater potential CO
2
reductions. For example,
air emissions reductions can be achieved through speed reductions, as studied by IMO
and as implemented through voluntary agreements with industry (Skjølsvik et al., 2000;
Corbett, 2004; Los Angeles Board of Harbor Commissioners et al., 2001). For a given
vessel, 10% reduction in speed (e.g. from 22 to 20 knots) can reduce energy requirements
for that voyage by more than 20%. Importantly, operational measures can also reduce air
quality pollutants such as NO
x
and SO
x
(both of which have climate-scale in
fl
eet and logistics planning, o
ff
uences
through ozone and aerosols).The IMO study estimated CO
2
reductions from operational
changes to range from 1 to 40%.
fl
