What's the next big thing in reducing
automotive CO2? Actually, there are lots of things, but one will be the
production of hydrogen green steel (H2GS), a new method of steel making
that has the potential to produce CO2-free steel. First off the blocks with an
H2GS pilot plant is SSAB, a Swedish steel maker backed by Mercedes-Benz, which
has taken an equity stake in the company.
Steel is an essential material but
manufacturing it generates huge amounts of CO2, with one estimate ranking it as
being responsible for 6%-7% of global greenhouse emissions. The process of
smelting the basis of steel, pig iron, from iron ore yields more than 1.7
tonnes of CO2 for every single tonne of finished steel produced.
Where does the CO2 come from?
Not just from the amount of energy used in production. In fact, most of it
comes from the chemical reaction that takes place during the smelting of the
ore. Steel is an alloy of pig iron, carbon and other additives to make
different kinds of steel. For example, adding chromium to the mix makes
stainless steel. Steel starts life as iron ore – iron oxide (rust) embedded in
rock.
The first stage is to make pig iron from
the iron ore in a blast furnace. The ore is mixed with high-grade coke (made by
heating coal to high temperatures) and oxygen is blasted through it to
generate very high temperatures. The coke, which has a high carbon content,
burns to produce carbon monoxide (CO). Then the oxygen atoms from the iron
oxide combine with the CO to make CO2. Further processes follow to turn
the pig iron into steel alloy but it’s this initial stage of producing pig iron
that is the main culprit in generating CO2.
It may seem as though the link between
CO2 and steel making is a bullet that can’t be dodged, but H2GS is made using a
new method called hydrogen direct reduction (H-DR). In chemistry, the process
where an oxide like iron oxide has the oxygen atom removed to leave iron is
called reduction. It’s the opposite of oxidation, where, for example, an
oxygen atom combines with iron to produce iron oxide. When steel objects
rust, they are oxidising.
H-DR means that instead of a two-stage
reduction, where CO is produced first and then pinches an oxygen atom from the
iron oxide to make CO2 and pig iron, hydrogen used to fire the furnace combines
directly with the iron oxide to make water and pig iron, but no CO2. SSAB,
along with LKAB and Vattenfall, has been working on the concept since 2016,
when the trio kicked off a joint-venture project called Hybrit. The goal
is to make steel fossil free by 2035 and, by doing so, the joint venture
expects to reduce Sweden’s total CO2 emissions by 10% and Finland’s by 7%. To
be completely fossil free, all the energy used, including the production of
hydrogen, must come from renewable sources.
www.autocar.co.uk