Process-Related Emissions in the Industrial Sector
Carbon dioxide emissions in the industrial sector result from both energy
use and production processes. Together, energy- and process-related emissions
in the industrial sector account for about one-fourth of global carbon
dioxide emissions.a Process-related emissions are a direct byproduct of
production. Because releases of carbon dioxide are inherent in the production
of iron and steel, cement, and aluminum, the potential for reducing process-related
emissions is limited. As a result, carbon abatement will face significant
technological challenges in the industrial sector. In addition, there are
no economical substitutes for these materials or their production processes,
and none is likely be available in the near term.
The largest carbon dioxide emitter in the industrial sector is the iron
and steel industry. In addition to being tremendously energy-intensive,
the blast furnace process for steel production generates carbon dioxide
directly. When super-heated oxygen (O) is blown into a blast furnace containing
coal coke and iron oxide (FE2O3), the oxygen fuses with carbon in the coke
to produce carbon monoxide (CO) which, at high temperatures, reduces iron
oxide by removing the oxygen to produce pure molten iron (Fe) and carbon
dioxide. The primary chemical reaction involved in the process is:
Two-thirds of the world’s steel production uses blast furnaces, including
90 percent of the steel made in China, which is the world’s fastest-growing
steel producer.b
The situation is similar in the cement industry. The primary ingredient
in marketed cement is cement clinker, composed largely of calcium oxide
(CaO). Clinker is produced by superheating quarried and ground raw materials
in a massive kiln. The most abundant material in the process is limestone
(CaCO3). The chemical reaction involved in heating limestone is:
Although there are many possible ways to improve energy efficiency in the
cement production process, the
fundamental chemistry of producing cement clinker will always result in
direct emissions of carbon dioxide. Cement industry groups point out that
cement and concrete are important components of environmentally friendly
development because of their durability and energy performance.c To the
extent that that is true, demand for cement is likely to remain strong
even in the most carbon-constrained future scenario, and direct emissions
from cement production will remain an issue.
The basic process involved in producing aluminum also emits carbon dioxide
directly. Aluminum is produced by running an electrical current through
a molten mixture of electrolyte and refined alumina (Al2O3). In the process,
carbon (C) from a graphite anode fuses with and removes oxygen from the
alumina to produce molten aluminum metal. A simplified version of the reaction
is:
Just as cement will continue to be a component of energy efficiency improvements
in the buildings sector, aluminum will play a role in reducing fuel use
in the transportation sector. Specifically, fuel economy is substantially
improved when aluminum is used to reduce the weight of vehicles. Although
aluminum production from recycled scrap metal would avoid most of the process-related
emissions, most of the aluminum sold in world markets probably will come
from primary production for the foreseeable future.
The inability of major energy users (and carbon dioxide emitters) in the
industrial sector—including the iron and steel, cement, and aluminum industries—to
remove carbon dioxide from their production processes limits their ability
to respond to climate change initiatives. The situation is further complicated
in that demand for their products is unlikely to subside in the near future.
As a result, policy regimes insituted by OECD nations to address carbon
dioxide emissions already have begun to afford those industries special
treatment.
aInternational Energy Agency, Energy Technology Perspectives: Scenarios
and Strategies to 2050 (Paris, France, June 2008), p. 471.
bWorld Steel Association, “World Steel in Figures 2008” (2008), web site
www.worldsteel.org/pictures/publicationfiles/ WSIF%202008%202nd%20edition.pdf.
cPortland Cement Association, “Sustainable Development” (2008), web site
www.cement.org/newsroom/newsroom_reference_ sustain.asp. |