In
our top read this week, The New Yorker's Matthew
Hutson examines a new manufacturing technique
that could drastically reduce the footprint of one
of our dirtiest materials.
Steel
production accounts for around 7% of
humanity’s greenhouse-gas emissions. There are two
reasons for this startling fact. First, steel is
made using metallurgic methods that our Iron Age
forebears would find familiar; second, it is part
of seemingly everything, including buildings,
bridges, fridges, planes, trains, and automobiles.
According to some estimates, global demand for
steel will nearly double by 2050. Green steel,
therefore, is urgently needed if we’re to confront
climate change.
Sometime around 2000 BCE,
it was discovered, possibly by accident, that
iron-heavy rock, or ore, became malleable when it
was heated over charcoal fires. Today, we can
explain why this happens: at high enough
temperatures, iron atoms loosen their grip on
oxygen atoms. The oxygen binds to the carbon in
the charcoal, forming CO2, which flies off into
the air. What’s left behind is purified, or
“reduced”, iron. The process of reduction allowed
the Iron Age to begin.
It’s hard to say
exactly when steel was first made. From time to
time, it would be created when carbon diffused
from the charcoal into the iron, strengthening it.
But steel production was hard to control until a
few hundred years ago, when the blast furnace was
invented. Using bellows, steelworkers increased
the temperatures of their coal fires to nearly
3,000 degrees – hot enough to melt iron in
large quantities.
Today, blast furnaces are
still the main method used to reduce steel.
Current models are about a hundred feet tall, and
can produce ten thousand tons of iron in a day.
Instead of charcoal, they use coke, a processed
form of coal. Coke and ore go in the top of the
furnace, and molten iron comes out the bottom,
infused with carbon; this iron can be easily
processed into steel. The steel industry produces
around two billion tons of it each year, in a
$2.5-trillion market, while emitting more than
three billion tons of CO2 annually, most of it
from blast furnaces.
Fortunately, we’ve
since learned that there’s more than one way to
purify iron. Instead of using carbon to remove the
oxygen from ore, creating CO2, we can use
hydrogen, creating H2O – that is, water. Many
companies are working on this approach; this
summer, a Swedish venture used it to make steel at
a pilot plant. If the technique were widely
employed, it could cut the steel industry’s
emissions by 9%, and our global emissions by
nearly 6%. That’s a big step toward saving the
world. |
