33
2.9 Burning Fossil Fuels Releases Stored
Carbon-Based Energy
Carbon when combined with oxygen and a source of ignition produces a strong
exothermic reaction. It releases a lot of energy. Coal is approximately 50% pure
carbon. Carbon-based life itself is possible only through the hydrogenation of carbon dioxide. Organic chemistry is separate from inorganic chemistry in that it studies organic molecules that always contain carbon and usually hydrogen. Inorganic
chemistry is concerned with inorganic reactions and molecules that usually don’t
contain carbon.
Since all life on earth is carbon based, it is impossible to support wholesale vilification of this element. That said, higher levels of atmospheric inorganic carbon
compounds especially carbon dioxide (CO 2 ) and methane (CH 4 ) are identified as
greenhouse gasses and implicated as climate change drivers.
High-energy industrial processes, such as the manufacturing of steel, concrete,
and paper, the refining of fuels, the production of fertilizers and other chemicals,
and large-scale electricity generation to power the gird, require a steady supply of
high exergy fuel. Each fuel has a specific energy, which is the amount of energy
embodied in the mass of a substance; it is measured in megajoules per kilograms
(MJ/kg). A fuel’s energy density is the amount of energy contained in a bounded
volume of a substance, such as a tank holding a fuel, measured in megajoules
per MJ/kg.
Figure 2.2 shows the comparison of both specific energy and energy density for
a range of different fuel types. It is clear from this graphic comparison why coal, as
well as liquid hydrocarbons, drives modern civilization. The relative convenience,
transportability, transformability, and safety that different forms of energy provide
are key drivers of any fuel’s utility and popularity. Uranium 235, for instance, boasts
specific energy of over 83,000,000 MJ/kg, an energy density of 7.4295E+10 MJ/m
3
,
and zero CO 2 emissions. There are significant associated process complexity
involved in splitting uranium atoms to yield energy, high facility costs, and problems with radioactive waste disposal afterward. Uranium is, therefore, not as widely
used as high carbon content coal with its comparative paltry specific energy six
orders of magnitude lower, at 30 MJ/kg, and its high CO 2 emissions.
2.10 Matter Is Embodied Energy
For the designer, the matter/energy connection is significant beyond the fact that it
takes energy to manufacture goods. At the smallest elemental scale, energy is constantly being exchanged and transformed. This fact makes “net zero energy” products, in the strictest sense, at once impossible and unavoidable. Whether any good
or service can be considered net zero depends on the boundaries that define the
accounting and the scale of what is being measured. This is useful to designers
2.10 Matter Is Embodied Energy
2.9 Burning Fossil Fuels Releases Stored
Carbon-Based Energy
Carbon when combined with oxygen and a source of ignition produces a strong
exothermic reaction. It releases a lot of energy. Coal is approximately 50% pure
carbon. Carbon-based life itself is possible only through the hydrogenation of carbon dioxide. Organic chemistry is separate from inorganic chemistry in that it studies organic molecules that always contain carbon and usually hydrogen. Inorganic
chemistry is concerned with inorganic reactions and molecules that usually don’t
contain carbon.
Since all life on earth is carbon based, it is impossible to support wholesale vilification of this element. That said, higher levels of atmospheric inorganic carbon
compounds especially carbon dioxide (CO 2 ) and methane (CH 4 ) are identified as
greenhouse gasses and implicated as climate change drivers.
High-energy industrial processes, such as the manufacturing of steel, concrete,
and paper, the refining of fuels, the production of fertilizers and other chemicals,
and large-scale electricity generation to power the gird, require a steady supply of
high exergy fuel. Each fuel has a specific energy, which is the amount of energy
embodied in the mass of a substance; it is measured in megajoules per kilograms
(MJ/kg). A fuel’s energy density is the amount of energy contained in a bounded
volume of a substance, such as a tank holding a fuel, measured in megajoules
per MJ/kg.
Figure 2.2 shows the comparison of both specific energy and energy density for
a range of different fuel types. It is clear from this graphic comparison why coal, as
well as liquid hydrocarbons, drives modern civilization. The relative convenience,
transportability, transformability, and safety that different forms of energy provide
are key drivers of any fuel’s utility and popularity. Uranium 235, for instance, boasts
specific energy of over 83,000,000 MJ/kg, an energy density of 7.4295E+10 MJ/m
3
,
and zero CO 2 emissions. There are significant associated process complexity
involved in splitting uranium atoms to yield energy, high facility costs, and problems with radioactive waste disposal afterward. Uranium is, therefore, not as widely
used as high carbon content coal with its comparative paltry specific energy six
orders of magnitude lower, at 30 MJ/kg, and its high CO 2 emissions.
2.10 Matter Is Embodied Energy
For the designer, the matter/energy connection is significant beyond the fact that it
takes energy to manufacture goods. At the smallest elemental scale, energy is constantly being exchanged and transformed. This fact makes “net zero energy” products, in the strictest sense, at once impossible and unavoidable. Whether any good
or service can be considered net zero depends on the boundaries that define the
accounting and the scale of what is being measured. This is useful to designers
2.10 Matter Is Embodied Energy