Environmental Engineering Reference
In-Depth Information
bonds and a material that is very strong in compres-
sion but has hardly any tensile strength and hence has to
be reinforced for most construction uses. Such a compos-
ite material (its diffusion began after 1880) has mono-
lithic qualities, and it can be fashioned into almost any
shape.
Global cement production reached 1.86 Gt in 2003,
with China accounting for 40% of the total and India
and the United States being distant second and third
(USGS 2006). Cement production starts with raw mate-
rial preparation (crushing, drying, and raw grinding),
clinker is made by firing in large kilns (the most energy-
intensive part of the process), and final ball milling yields
the finished material. The net theoretical minimum
needed to produce clinker is about 1.75 GJ/t, and the
lowest reported industrial values cluster at about 2.9
GJ/t; depending on the process and the principal fuel
used (coal or natural gas), most of the published values
are 3.2-7 GJ/t (DOE 1997; Sheinbaum and Ozawa
1997; Tresouthick and Mishulovich 1991). After mixing
with water and aggregate (sand or gravel that costs little,
@100 MJ/t), concrete embodies 1-2 GJ/t and rein-
forced concrete that includes 100 kg/m
3
of steel bars
embodies 2-3 GJ/t.
Energy intensity of three traditional construction
materials is fairly similar. Fired clay bricks need 4-8
GJ/t (sun-dried bricks, common in the antiquity, are
now used only by peasants in the poorest countries);
gypsum needs as little as 3 GJ/t; and U.S. drywall (gyp-
sum between paper boards) needs up to 6 GJ/t. The
energy cost of stone quarrying is commonly less than 1
GJ/t, but transportation costs, particularly for large
pieces, can multiply that value severalfold. The energy
cost of lumber reflects a difference in harvested stands
(climax vs. immature, native vs. plantation, hardwood vs.
softwood), harvesting techniques, and the extent of pro-
cessing and drying. Costs are as low as 0.57 GJ/t and
as high as 41.2 GJ/t, but most rates fall between 0.6
GJ/t and 9 GJ/t; those between 2 GJ/t and 7 GJ/t
(including kiln drying) are perhaps the most representa-
tive (Glover, White, and Langrish 2002; CWC 2004;
Buchanan and Honey 1994). Chipping, gluing, and
compressing raises the cost of particle board to 8 GJ/t
and of plywood to at least 10 GJ/t.
Iron remains by far the most important metal
extracted from the crust. Worldwide iron ore production
surpassed the 500-Mt mark in 1960 and reached 1.2 Gt
by 2003. Smelting of pig iron topped 700 Mt in 2004,
and nearly all this metal is processed into steel. With the
addition of 400 Mt of steel scrap, the global production
of crude steel surpassed 1 Gt in 2004 (IISI 2005). Steel
provides a large part of the physical infrastructure of
modern civilization as well as a high-quality, relatively
inexpensive and durable material for manufacturing an
enormous variety of products, including all the essential
machinery for energy industries. Rapid diffusion of coke-
based iron ore smelting after 1750 was accompanied by
an impressive decline in specific coke consumption; a
rich retrospective literature (Bell 1884; King 1948; Hyde
1977; Gold et al. 1984) enables us to follow the subse-
quent progress.
Technical advances lowered typical energy costs of pig
iron from nearly 300 GJ/t during the late eighteenth
century to less than 100 GJ/t during the 1840s and
about 50 GJ/t by 1900. By 1950 the best rates were
about 30 GJ/t, and during the late 1990s the net specific
energy consumption of modern blast furnaces was be-
tween 12.5 GJ/t and 15 GJ/t (de Beer, Worrell, and
Blok 1998), or roughly twice the theoretically lowest
amount of energy (6.6 GJ/t) needed to produce iron
