Environmental Engineering Reference
In-Depth Information
Table 12.2
Energy intensity for the manufacture of food packages.
Package
Energy (MJ)
Styrofoam tray (size 6)
0.90
Molded paper tray (size 6)
1.61
Polyethylene pouch (16 oz, or 455 g)
2.34
Steel can, aluminum top (12 oz)
2.38
Steel can, steel top (16 oz)
4.21
Glass jar (16 oz)
4.28
Coca-Cola bottle, nonreturnable (16 oz)
6.16
Aluminum can, pop-top (12 oz)
6.88
Plastic milk container, disposable (1/2 gal)
9.04
Polyethylene bottle (1 qt)
10.44
Polypropylene bottle (1 qt)
11.52
Adapted with permission from Pimentel and Pimentel, 2008.
Steel
Steelmaking is not as energy intensive as aluminum production, but still iron and steel manu-
facturing is the largest energy consumer among all manufacturing industries (Strezov, 2006).
Energy spent per metric ton of steel produced depends on the method and concentration of the
ore (Table 12.3). On average, 24 GJ are spent per metric ton to produce steel on a worldwide
basis. Most energy-efficient processes use 19 GJ/tonne for primary steel and 7 GJ/tonne for
secondary steel manufacturing (de Beer et al., 1998). Parker (1991) reports 27 GJ/tonne, and
the American Iron and Steel Institute (AISI) states that in the United States on average, the
energy intensity for steel production is 14.6 GJ/tonne (12.6 10
6
Btu/short ton), shipped 22.7 GJ/
tonne (19.55 10
6
Btu/ton) for integrated steelmakers, and 6.1 GJ/tonne (5.25 10
6
Btu/ton) for
electric steelmakers (AISI, 2005).
Besides energy spent during steel manufacturing, additional energy is needed to transform
the liquid steel into a strip, and before forming the metal into cans, a protective layer of tin or
other surface coating material needs to be added. Boustead and Hancock (1981) estimate
5.88 MJ/kg (5880 MJ/tonne) is the energy spent to transform liquid steel into a hot rolled slab
that is subsequently formed into a strip.
Tin coating takes place in a separate facility from where the hot rolled strip is produced. It
takes approximately 10 MJ to produce 1-kilogram of tin-coated steel and 8.6 MJ to produce
1-kg of tin-free steel, which is protected by a chrome layer, from a hot rolled coil (Boustead
and Hancock, 1981).
Furthermore, to avoid internal corrosion and contamination of the food product with dis-
solved metal, interior surfaces of cans are coated with an organic coating. There are several
coating types, such as vinyls, varnishes, and lacquers. The energy intensity to produce an alkyd
varnish is 268 MJ/kg and for an epoxy lacquer 376 MJ/kg (Boustead and Hancock, 1981).
With all the factors involved in producing the materials and forming the container, a 16-oz
steel can needs about 4.21 MJ (Pimentel and Pimentel, 2008).
Petroleum-based plastics
Petroleum-based plastics have the dual impact of using nonrenewable energy (in most cases)
plus the use of the feedstock that otherwise would be used as fuel. To make 1-kg of PET, it
takes 37 MJ of energy and the equivalent of 39 MJ of petroleum-derived raw materials totaling
76 MJ/kg (Gerngross and Slater, 2000). Then, turning PET into bottles takes another 20 MJ/kg
per finished bottle (Gleick and Cooley, 2009).
