In 2015, the cement sector generated nearly 3bn tonnes of carbon dioxide, equivalent to 8% of the global total. Its footprint is eclipsed by iron and steelmaking – thought to be the single-largest source of industrial pollution, with up to 9% of all direct emissions from fossil fuels.
Many industrial processes require vast quantities of thermal energy at extremely high temperatures. Today, fossil-fuel combustion is still the preferred way to produce this heat. But if governments are serious about their commitments under the Paris agreement, industrial titans will have to figure out how to decarbonise their production processes – and fast.
There’s no single, readily available solution to the issue of industrial pollution. Each sector will have to plot its own course to a zero-emissions future. In some cases, this will involve developing entirely new technologies and ways of working. The need for innovation is acute in both the steel and cement industries, which are contending with ballooning demand from emerging economies with ambitious infrastructure plans.
Cement
China famously used more cement between 2011 and 2013 than the US used in the whole of the 20th century. And the country still leads the world in consumption of the key building material. Cement has a very serious flaw in the form of hard-to-abate process emissions. The root of the problem is clinker, the binding agent in almost all cement.
“Clinker is produced through the calcination of limestone, requiring high temperatures, about 1,400°C, for the chemical reaction to take place,” explained Markus Hagemann, co-founder of the NewClimate Institute, a policy research organisation. “The chemical process itself produces process emissions containing CO2. These process emissions typically account for more than 50% of cement emissions, while the heating of the clinker kiln accounts for about 40% of the emissions, as coal is the most commonly used fuel to heat the kiln.”
Reducing the use of clinker, through adding substitutes such as clay, is an obvious place to start. However, this wouldn’t fully decarbonise cement production. Doing so might mean ditching clinker altogether in favour of “novel” cements that use alternative binding agents. When it comes to the crunch, climate policies may compel the construction sector to deploy different materials altogether.
While progress in cement has been slow, there are some encouraging signs that the industry is taking its environmental obligations seriously. One feasibility study carried out by Swedish power company Vattenfall and construction firm Cementa found that it was technically possible to electrify the heating part of the cement-making process. The companies now want to look into building a pilot plant that would use renewable electricity to heat a kiln.
Steel
There could also be a role for electrification in steelmaking, another process that depends heavily on the combustion of coal. Roughly two-thirds of steel is produced through the blast furnace/basic oxygen furnace system (BF-BOF), in which iron ore is “reduced” in a blast furnace to create pig iron, and then transformed into steel in an oxygen furnace. But the carbon-intensive reduction step can be skipped if scrap steel is smelted in an electric arc furnace. This method only requires about one third of the energy used in the BF-BOF route.
As its name suggests, an electric arc furnace is fed by electricity, and, if that electricity has been generated using wind and solar power, the grey metal suddenly gains a green sheen. It’s also possible to replace coal – the reducing agent in the pig iron manufacturing process – with hydrogen.
It will still react as necessary with the oxygen in the iron ore, but the result is water vapour and not CO2. If the hydrogen itself is produced using renewable energy, the emissions outlook for steel looks brighter still.
Earlier this year, German steelmaker Thyssenkrupp announced that it plans to utilise a hydrogen-based process across its operations by 2050. Not to be outdone, Svenskt Stål, also known as Swedish Steel, has pledged to have its own fossil-free, hydrogen-fuelled products on the market by 2026.
“Most likely, in a mid- to long-term perspective, a combination of technologies will play an important part in decarbonising the iron and steel sector, putting pressure on the transformation of the energy sector to provide large-scale availability of clean hydrogen and electricity,” Hagemann predicted.
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