Oct 08 2007

Behind the Shining: Aluminum’s Dark Side

PFCs

In 1991, Dr. Dean Abrahamson of the University of Minnesota discovered that

primary aluminum smelters produce two extremely potent greenhouse gases:

tetrafluoromethane and hexafluoroethane.

With atmospheric lifetimes are at least 10,000 years, these are some of the

longest-lived atmospheric pollutants. The gases have global warming

potentials that are 6,500 to 9,200 times higher than carbon dioxide. The

emission of one kilogram of tetrafluoromethane would have the same climate

change effect, over the subsequent 100 years, as 6.5 metric tons of carbon

dioxide. (“Greenhouse worries for the aluminum industry,” Energy, Economics

and Climate Change, Jan. 1992; Harnisch et al.)

The MIT scientists suggested that “in view of the PFCs’ atmospheric

stability and their large specific radiative forcing relative to most other

greenhouse gases, increased scientific focus on these compounds is

warranted.” (Harnisch et al.)

These two gases are the unintentional byproduct of using fluorine in the

electrolytic reduction of alumina, formed during the “anode effect,” when

the electrolyte is depleted.

Harnisch, et al, estimate that each of ton of aluminum production created

about 0.48 kilograms of tetrafluoromethane in 1995. Technological

improvements brought this level down 30 percent from emission rates in the

1980s. Still, the primary aluminum industry generated about 9,400 tons of

this PFC in 1995, or about 90 percent of all tetrafluoromethane emissions

worldwide. This is the global warming equivalent of 59.22 million metric

tons of carbon dioxide.

The MIT study further estimates that in 1992, aluminum smelters emitted

about 1,300 tons of hexafluoroethane, or the greenhouse gas equivalent of

11.96 million tons of CO-2. Primary aluminum production accounted for about

65 percent of this chemical’s total emissions; plasma etching in the

semiconductor industry accounted for the balance of hexafluoroethane

emissions..

Proportionally, smelters employing Vertical Stud Soderberg and Sidework

Prebaked technology account for most of the industry’s PFC emissions. The

MIT study estimated that in 1995, these two technologies generated 65

percent of emissions even though they accounted for only 30 percent of

production. (Harnisch et al)

The International Aluminium Institute uses a grouping of technologies.

First generation plants built between 1940 and 1955 emit between 12-15

kilograms of PFCs per ton of metal produced; those built between 1955-75

emit 2-6 kilograms per ton; and “third generation plants” (1975-today),

emit from 0.3 to 1 kilogram per ton. (Interantional Aluminium Institute,

“Smelter emissions,” on its website, world-aluminium.org)

Pages: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25

Leave a Reply

Náttúruvaktin