Environmental Engineering Reference
In-Depth Information
kg) for iron smelting has accounted for an increasing
share of consumed phytomass.
Traditional charcoaling was very wasteful (5-6 kg of
wood/kg of charcoal), as was primitive iron smelting
(up to 600 MJ/kg of metal). These demands led to ex-
tensive deforestation throughout Europe and Asia. By
the end of the eighteenth century the iron smelting rate
was below 250 MJ/kg, and the best charcoal-fueled blast
furnaces of the twentieth century needed less than 30
MJ/kg. The introduction of coke was one of the two
major reasons for rapid expansion of coal mining; wide-
spread adoption of the steam engine was the other. This
was a profound change. Earlier societies had been ener-
gized by virtually instantaneous solar flows, whereas coal
mining laid the foundation for a civilization supported by
accumulated stores of fossil fuels. Withdrawals of this fuel
capital have energized the exponential increase in global
population through unprecedented improvements of ag-
ricultural productivity, and have led to large increases in
material affluence among the richest one-fifth of human-
ity as well as to the globalization of human affairs.
In 1800 global phytomass combustion surpassed the
burning of coal tenfold; by 1900 the gross energy con-
tent of biomass energies was equal to that of fossil fuels;
and by 2000 fossil fuels contributed 1 OM more than
biomass (fig. 13.5). Because of the superior conversion
efficiencies of fossil fuel combustion (on the average at
least four times that of preindustrial burning of phyto-
mass), coals, oils, and gases have come to contribute
about 40 times more useful energy than plant matter.
This dominance has had far-reaching effects on the struc-
ture and functioning of human societies. Ours is a fossil-
fueled civilization, and its dependence on coals and
hydrocarbons
Resources that molded our civilization are mineraloids
of organic origin (though perhaps some are abiogenic)
containing variable shares of moisture, trace elements
(notably S and N), and incombustible ash. Energy den-
sity is just 8 MJ/kg for the poorest lignites, and it goes
up to 36 MJ/kg for the best anthracites. Standard bitu-
minous coal has 29 MJ/kg, most steam coals 20-25
MJ/kg. Complex hydrocarbons give more homogeneity
to crude oils; their energy density is 42-44 MJ/kg, and
that of natural gases 30-45 MJ/m
3
(3 OM less than that
of liquid fuels). Total resources of these fuels are uncer-
tain, but in 2005 proved recoverable stores of all conven-
tional fossil fuels added up to some 30 ZJ, and ultimate
recovery estimates were more than twice as large.
Global coal reserves recoverable with current tech-
niques amount to some 160 years of 2005 production.
In 2005 the global R/P ratios for crude oil and natural
gas were about 40 and nearly 70 years respectively, but
considerable uncertainties regarding ultimately recover-
able hydrocarbon reserves make it impossible to pinpoint
cannot be
shed without profoundly
13.5 Global consumption of biomass and fossil fuels, 1700-
2000. From Smil (2003).
reshaping the entire society.
