Geology Reference
In-Depth Information
3.6 Summary of the chapter
Throughout this chapter, a review of the main thermodynamic properties required
for a physical assessment of mineral resources has been carried out.
Particularly, it has been seen that the First Law (or law of conservation) and
its associated property, energy, is not suitable for sustainability accountancy as it
is not able to categorise resources according to their quality. Hence, one needs to
resort to the Second Law and the entropy property. But even if entropy is sensitive
to quality, it is a measure of disorder and therefore is an abstract and not very
practical property.
Exergy combines both laws and is capable of simultaneously expressing the
quantity and quality of any resource. It is additive and as opposed to entropy
is expressed in more understandable units (energy units). Moreover it has the
ability to objectify all the physical characteristics of resources, independently of
their market value.
Exergy content alone is however not suitable as an indicator for resource ac-
counting, as it would consider all resource generation processes to be reversible.
So, if resources were assessed with exergy, the values obtained would be extremely
low. This is because all real processes are irreversible. Hence, even if exergy is the
starting point for the assessment, it is exergy cost that provides information which
is closer to Man's perception of value. The concept of exergy cost is defined as the
amount of the resources measured in exergy terms required to build a product. It
thus involves all irreversibilities that appear in the process and as a result can be
tens to thousands of times greater than the exergy of the same product.
Exergy cost is the key concept of Thermoeconomics, i.e. the branch of knowledge
of energy saving. This novel discipline connects the universal measure of physical
loss, i.e. irreversibility with the loss of resources and then with Economics. Thermo-
economics has been widely used for optimising and improving industrial processes.
However its potential for natural resource assessment has not been su ciently ex-
ploited.
The authors thus propose the Exergoecology approach, which derives from Ther-
moeconomics and attempts to assess natural resources through the so-called exergy
replacement costs. This topic specifically looks at the mineral endowment on Earth,
which falls under Physical Geonomics (a branch of Exergoecology). Physical Geo-
nomics assesses the degradation of mineral resources according to the exergy re-
quired to return them from a completely dispersed state to the conditions of com-
position and concentration originally found in Nature. This is further explored in
the next chapter.
 
Search WWH ::




Custom Search