Environmental Engineering Reference
In-Depth Information
when the climate was tropical across much of the planet and atmospheric CO
2
concentrations
were very high. This storing of carbon through the growth of plant matter, and its subsequent
conversion to coal, oil, peat and gas, dramatically reduced atmospheric CO
2
levels and
played an important role in cooling the planet to temperatures that could support advanced
life forms. The concern now is that by unlocking this stored carbon climate change is being
driven in the other direction, with global warming the direct result of an excessive greenhouse
effect.
Ice core samples indicate that the level of carbon dioxide in the atmosphere was more or
less stable at 280 parts per million (ppm) over the last few thousand years up to the onset of
the industrial revolution at the beginning of the nineteenth century. Subsequently, atmo-
spheric CO
2
levels rose, at fi rst slowly as a result of coal burning but since the Second World
War the release of CO
2
has accelerated refl ecting the exploitation of a wider range of fossil
fuels. Current CO
2
levels are 380 ppm and rising fast.
CO
2
is not the only pollutant created by fossil fuelled generation: combustion in air com-
prising 78% nitrogen by volume inevitably produces nitrogen oxides, NO, and NO
2
and N
2
O,
collectively known as NO
x
; and any sulfur content of the fuel results in SO
x
emissions. NO
x
and SO
x
together contribute to acid rain and as a result it is now common to reduce any SO
x
emissions from fossil fuelled power stations through fl ue gas desulfurization. The downside
of this is reduced thermodynamic effi ciency and some resulting increase in CO
2
emissions.
World coal reserves are substantial, but coal is a less attractive fuel from the point of view
of CO
2
emissions and also much more disruptive to extract. The cheapest coal is from
opencast mines, but this process is immensely damaging to the environment. All forms
of generation have some environmental impact, but these are not in general refl ected in the
cost of electricity; because of this, these additional environmental costs are known as
externalities
.
Externalities are consequences of activity that are not normally a part of the economic
analysis; for example the cost to society of ill health or environmental damage arising from
pollution caused by a specifi c generating plant is not directly charged to the operator, i.e. it
is external to the microeconomics of the plant's operation. A number of European countries
now seek to bring these externalities back into the economics of electricity generation by
some kind of environmental levy or carbon tax. Carbon trading, discussed in detail in Chapter
7, is an alternative means of achieving this goal.
The nuclear cycle is of course not without externalities, although the environmental costs
are highly contested, contributing as they do to the economic attractions or otherwise of
nuclear power. Radioactive waste disposal, radioactive emissions and fi nal decommissioning
and disposal of radioactive reactor components are rarely fully accounted for and thus fall to
an extent into the category of externalities. There are also issues concerned with environmen-
tal damage associated with uranium mining, but in this regard it is similar to coal. If nuclear
power is to mitigate global emissions, it is of vital importance to assess accurately how much
CO
2
will be displaced by nuclear power. This is a topic fraught with controversy. The well
established 386 g CO
2
/kW h contributed by gas fuelled power stations will be taken as the
benchmark. The emissions for nuclear power are quoted as 11-22 by OECD, and 10-130 by
ISA, University of Sydney [3]. If the upper fi gures are valid, the contribution of nuclear power
to CO
2
mitigation may be seriously compromised. Clearly this is an issue that requires
certainty.
