Geology Reference
In-Depth Information
take care of it, not just for the benefit of the current generation but also the many
after it. To be able to do this one must first understand the effect that society is
having on the health of the planet and its resources and how to reduce it. And this
takes more than nice words in global conferences - it requires measuring units and
reference frameworks.
Furthermore and with good reason, it is the physical not the economic which
must serve as the reference point, as it is the latter which is subject to the former
and not the other way round. Apart from that, no single currency has stood the
test of time, which begs the question: how does one reliably measure the disper-
sion of societal mineral stock, or the exhaustion of mines? How can one fairly or
adequately account for the use of energy, water or soil? All such questions find
their answer in the use of one universal unit of measure, exergy. Exergy has the
ability to undertake the global and intergenerational analysis that monetary units
simply cannot. It can also quantitatively demonstrate the effect of waste, mine
extraction, water consumption or soil erosion on resource stocks, which can then be
extrapolated to indicate those risks posed on society, should they continue or even
accelerate. This is because it is the variation of an intensive property with respect
to a reference environment, which exergy quantifies in SI units (e.g. kJ). This then
means that the same unit with which one measures energy, can also be used to mea-
sure materials. This then serves to avoid the possibility of trying to add apples to
oranges. Moreover, processes involving mixing and separation, manmade as much
as natural, can also be measured in terms of exergy loss, even if there are no energy
losses. In addition, as the exergy of a fuel is approximately equal to its high heating
value, one can reference exergy in terms of toe (tonnes of oil equivalent) or any
other conventional energy unit, whilst maintaining the scale used by a practitioner.
It also permits the addition of different kinds of resources and supports dynamic or
cost benefit analysis as is done with money.
17.2.2 Abiotic resources are not well defined thermodynamic
systems
Exergy calculations are unfortunately far from simple. The use of exergy as a unit
of measure always requires the definition of two states: that of the product and that
of the reference environment or baseline. One must state the intensive properties
of the substances to be evaluated i.e. whether they are solid, liquid or gas, their
composition, concentration, temperature, height, speed, etc. The difference between
these intensive properties and those of the reference environment, converted into
energy terms, provides the overall exergy value between the two states.
This topic makes a conceptual leap: exergy can also be used to assess natural
resources. In an intuitive way, it stands that a mine, a cloud, a glacier, a river, a
metal or even a waste are abiotic resources clearly distinguishable from a completely
mixed “entropic soup”. These types of systems, including the reference environment,
 
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