Exergy evolution of the mineral capital on earth - circe

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6 STARTING POINT, OBJECTIVES AND SCOPE Odum [245], [246] proposed an original physical unit <strong>of</strong> measure for assessing resources and products based on <strong>the</strong> solar emergy joule (sej). Emergy analysis is a technique <strong>of</strong> quantitative analysis which determines <strong>the</strong> values <strong>of</strong> resources, services and commodities in common units <strong>of</strong> <strong>the</strong> solar energy it took to make <strong>the</strong>m. One <strong>of</strong> its fundamental organizing principles is <strong>the</strong> maximum empower principle. It is stated as “systems that will prevail in competition with o<strong>the</strong>rs, develop <strong>the</strong> most useful work with inflowing emergy sources by reinforcing productive processes and overcoming limitations through system organization”. To derive solar emergy <strong>of</strong> a resource or commodity, it is necessary to trace back through all <strong>the</strong> resources and energy that are used to produce it and express <strong>the</strong>m in <strong>the</strong> amount <strong>of</strong> solar energy that went into <strong>the</strong>ir production [42]. The solar emergy per unit product or output flow is called “solar transformity”, with units <strong>of</strong> seJ/J. Solar transformities have to be obtained for each commodity. Most transformities cannot be considered as universal, as <strong>the</strong> processes involved in <strong>the</strong> formation <strong>of</strong> <strong>the</strong> commodities differ, depending on <strong>the</strong> period <strong>of</strong> time and place considered. The emergy analysis owns two fundamental capabilities that we think are required to be used as a scarcity indicator: 1) it is based on <strong>the</strong> physical characteristics <strong>of</strong> <strong>the</strong> resource and 2) all resources are measured with a single unit. Generally, <strong>the</strong> emergy analysis can be successfully applied for renewable resources. However it is very questioned <strong>the</strong> applicability <strong>of</strong> this approach for <strong>mineral</strong> resources, where <strong>the</strong> sun has not played a central role in <strong>the</strong>ir creation. No matter how much solar energy is received from <strong>the</strong> sun, <strong>the</strong> quantity <strong>of</strong> gold or iron for instance on earth, will not change. Consequently, <strong>the</strong> rigorousness <strong>of</strong> <strong>the</strong> transformities for <strong>mineral</strong> resource assessment is doubtful. Hence, <strong>the</strong> emergy analysis is not suitable for <strong>the</strong> purpose <strong>of</strong> this PhD, which is <strong>the</strong> assessment <strong>of</strong> <strong>mineral</strong> resources. The physical features that make <strong>mineral</strong> resources valuable are: a particular composition which differentiates <strong>the</strong>m from <strong>the</strong> surrounding environment, and a distribution which places <strong>the</strong>m in a specific concentration. And <strong>the</strong>se intrinsic properties can be in fact evaluated from a second law <strong>of</strong> <strong>the</strong>rmodynamics point <strong>of</strong> view in terms <strong>of</strong> a single property: exergy. As it happens to emergy and unlike standard economic valuations, <strong>the</strong> exergy analysis gives objective information since it is not subject to monetary policy, or currency speculation. Fur<strong>the</strong>rmore, all natural resources can be assessed in terms <strong>of</strong> exergy and can be summed up. <strong>Exergy</strong> is a property <strong>of</strong> <strong>the</strong> resource and as such, <strong>the</strong> calculation methods are physically and ma<strong>the</strong>matically supported, as opposed to emergy. As explained in <strong>the</strong> next section, exergy is based on <strong>the</strong> notion <strong>of</strong> a reference environment, in which <strong>the</strong> quality and quantity <strong>of</strong> substances is fixed. Hence <strong>the</strong> analysis places value to resources depending on <strong>the</strong> level <strong>of</strong> departure from <strong>the</strong> defined reference environment. And, as opposed to <strong>the</strong> emergy analysis, whe<strong>the</strong>r <strong>the</strong> substances in it were created through <strong>the</strong> energy <strong>of</strong> <strong>the</strong> sun or through o<strong>the</strong>r processes is irrelevant and does not affect <strong>the</strong> final results.
<strong>Exergy</strong> and <strong>the</strong> assessment <strong>of</strong> natural resources 7 The exergy method is chosen in this PhD for assessing <strong>the</strong> <strong>evolution</strong> <strong>of</strong> <strong>mineral</strong> scarcity. In <strong>the</strong> next section, an overview <strong>of</strong> <strong>the</strong> different existing approaches connecting <strong>the</strong> entropy law with <strong>the</strong> consumption <strong>of</strong> resources is provided. 1.4 <strong>Exergy</strong> and <strong>the</strong> assessment <strong>of</strong> natural resources A fundamental law <strong>of</strong> nature (<strong>the</strong> first law <strong>of</strong> <strong>the</strong>rmodynamics), tells us that energy and matter can be nei<strong>the</strong>r created nor destroyed. The second law places additional limits on energy transformations and reflects qualitative characteristics. It states that energy can only be transformed by <strong>the</strong> consumption <strong>of</strong> quality. Locally, <strong>the</strong> quality can be improved, but this can only occur at <strong>the</strong> expense <strong>of</strong> a greater deterioration <strong>of</strong> <strong>the</strong> quality elsewhere. The level <strong>of</strong> quality deterioration or disorder is measured through <strong>the</strong> property entropy. Hence, <strong>the</strong> second law <strong>of</strong> <strong>the</strong>rmodynamics can be formulated as follows. In all real processes <strong>of</strong> energy transformation <strong>the</strong> total entropy <strong>of</strong> all involved bodies can only be increased or, in an ideal case, unchanged. Beyond <strong>the</strong>se conditions, <strong>the</strong> process is impossible even if <strong>the</strong> first law is fulfilled [39]. The combination <strong>of</strong> both laws indicates that it is not a question <strong>of</strong> <strong>the</strong> existent amount <strong>of</strong> mass or energy, but on <strong>the</strong> quality <strong>of</strong> that mass or energy, or in o<strong>the</strong>r words on its exergy content. Technically, exergy is defined as <strong>the</strong> maximum amount <strong>of</strong> work that may <strong>the</strong>oretically be performed by bringing a resource into equilibrium with its surroundings by a sequence <strong>of</strong> reversible processes. The exergy <strong>of</strong> a system gives an idea <strong>of</strong> its <strong>evolution</strong> potential for not being in <strong>the</strong>rmodynamic equilibrium with <strong>the</strong> environment. Unlike mass and energy, exergy is not a conserved property. It is an extensive property, with <strong>the</strong> same unit as energy. In all physical transformations <strong>of</strong> matter or energy, it is always exergy that is lost. <strong>Exergy</strong> analysis is a powerful tool for improving <strong>the</strong> efficiency <strong>of</strong> processes and systems. This leads to less resources to be used and <strong>the</strong> emission <strong>of</strong> less wastes to <strong>the</strong> environment. However it is a much more useful concept, and can be applied for resource accounting. All materials have a definable and calculable exergy content, with respect to a defined external environment. The consumption <strong>of</strong> natural resources implies destruction <strong>of</strong> organized systems and pollution dispersion, which is in fact generation <strong>of</strong> entropy or exergy destruction. Fur<strong>the</strong>rmore, exergy has <strong>the</strong> capability <strong>of</strong> aggregating heterogeneous energy and material assets. This is why <strong>the</strong> exergy analysis can describe perfectly <strong>the</strong> degradation <strong>of</strong> natural <strong>capital</strong>. For that reason, an increasing number <strong>of</strong> scientists, such as Szargut and coworkers [344], [338], [339], Brodianski [39], Wall [393], [394], [395], Rosen [289], [290], Dincer [76], Sciubba [299] or Ayres et al. [14] believe that exergy provides useful information within resource accounting and can adequately address certain environmental concerns. Additionally, different renowned studies have shown up <strong>the</strong> connection between economic scarcity and <strong>the</strong> entropy law. Some notable examples are briefly outlined next.
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Results 91 • The orders o
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Results 93 Table 3.5: Mineralogical
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Results 101 Table 3.6. Crustal abun
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106 THE RESOURCES OF THE EARTH Tabl
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108 THE RESOURCES OF THE EARTH nowa
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110 THE RESOURCES OF THE EARTH exce
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114 THE RESOURCES OF THE EARTH al.
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116 THE RESOURCES OF THE EARTH volu
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120 THE RESOURCES OF THE EARTH Coal
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132 THE RESOURCES OF THE EARTH ing
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134 THE RESOURCES OF THE EARTH •
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136 THE RESOURCES OF THE EARTH •
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Chapter 5 Thermodynamic models for
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The reference environment 143 5.2.1
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The reference environment 145 envir
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Chapter 6 The ther
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The properties of
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The exergy distance 229 However, an
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Chapter 8 The exergy evolut
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Final reflections 321 consequently
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332 CONCLUSIONS of
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336 CONCLUSIONS is lost. Therefore,
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338 CONCLUSIONS According to our ca
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340 CONCLUSIONS which it is based w
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342 CONCLUSIONS have associated an
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344 CONCLUSIONS dation velocity, <s
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346 CONCLUSIONS fuel composition th
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348 CONCLUSIONS The main activity t
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Appendix A Additional calculations
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Input data. Mineralogical compositi
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Exergy calculation
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Exergy calculation
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Australian fossil fuel production 4
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World’s fuel production 405 % <st
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World’s fuel production 407 A.8.4
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Fuel consumption in the</st
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Nomenclature, Figures, Tables and R
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416 NOMENCLATURE ˙D : Minimum exer
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418 NOMENCLATURE T : Temperature [K
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420 NOMENCLATURE r w : River water
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422 LIST OF FIGURES 7.1 Conceptual
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424 LIST OF FIGURES 8.21 Actual exe
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426 LIST OF TABLES 3.6 Crustal abun
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428 LIST OF TABLES 8.6 Specific exe
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