Aluminium
Feature Articles
How Green is ‘Green’ Aluminium
March 2021
Increasing awareness and activity relating to greenhouse gas emissions has seen companies start to burnish their green/environmental responsibility credentials.

Sometimes referred to as ‘solidified energy’, primary aluminium is one of the most energy intensive industrial-scale metals to produce. Australia’s CSIRO has estimated the total embodied energy of aluminium is 211 GJ/t (58.6MWh/t)—in comparison steel was estimated at 22.7GJ/t (6.31MWh/t). By far the largest proportion of this embodied energy comes from the electricity used in the smelting process. Major producers, in response to market demands for more environmentally responsible materials are increasingly looking to market a low-carbon aluminium product and are increasingly asking a premium for it.

 

 

Low carbon aluminium encompasses primary aluminium that has a CO2 footprint sufficiently below the current industry average as well as material with significant recycled content—recycled aluminium has a production energy intensity ~95% below that of primary metal. The benchmark for low-carbon primary metal appears to be <4 metric tonne of CO2 per tonne of aluminium, significantly below the industry average of ~11.5 metric tonnes of CO2 per tonne of aluminium produced (Coal powered sources, prevalent in China and Australia typically release 18-20 tonne of CO2 per tonne of aluminium).

Going green is emerging as a product differentiator. The major producers, outside China, are now marketing low-carbon aluminium products, or have at least indicated an intention to. Highlighting the fact that the metal is produced using electricity from low or zero-emission power sources (generally hydropower—some argue the focus on the emission benefit of hydropower underplays the environmental impact dams can have when assessing CSR).

 

 

Size Matters

Almost all existing low-carbon aluminium is produced at smelters associated with zero-emission hydropower electricity. It is currently the only renewable source capable of generating the required amount of power.

To get in on the action, producers in the Middle East have looked to—and noticed the size of the challenge—the other renewable electricity sources. The sheer magnitude of electricity required has found wind and solar wanting. Emirates Global Aluminium (EGA), to produce its ‘CelestiAL’ low-carbon product, has reached agreement with the Dubai Electricity and Water Authority, for the supply of 560MWh of power from the 1,013MW Mohammed bin Rashid Al Maktoum solar park. However, this is sufficient for producing just 40kt of CelestiAL from the company’s 2.6Mt of production capacity—just 1.5%.

Other producers in the region have looked into powering capacity expansion projects by solar. They have been abandoned the idea when a back of the envelope assessment of the associated solar park and necessary storage was determined. As such, low-carbon production volumes from the region will be limited.

 

What the Scope?

CO2 is the primary contributor to a smelters GHG emissions. Many countries and companies have adopted GHG emission standards outlined by the Greenhouse Gas Protocol. It classifies emissions across 3 scopes:

Scope 1: Direct emissions – emissions directly generated by a company.

Scope 2: Indirect emissions – emissions from (typically) generating electricity consumed by a company.

Scope 3:  Additional indirect emissions – value chain emissions – emissions from consumers utilising company output.

Covering the power generation, the Scope 2 emissions are the heavy hitter in aluminium production. The Scope 1 emissions are often overlooked in broad discussions. They shouldn’t be.

 

Don’t Mention the Anode

Given its energy intensity, understandably the carbon emissions of aluminium production typically focus on the source of a smelter’s electricity. As such, low carbon primary aluminium is typically associated with metal produced with power from a renewable, low-emission source i.e., will have very low Scope 2 emissions. However, the ubiquitous technology for producing primary aluminium, the Hall-Heroult process, involves a redox chemical reaction between alumina and the carbon anode which produces aluminium metal and carbon dioxide:

2Al2O3 + 3C→ 4Al + 3CO2

Up to 500kg of carbon anode is consumed per tonne of aluminium metal produced. The carbon dioxide directly produced in this process, a Scope 1 emission, ranges from 1.4-1.8t CO2 equivalent per tonne of aluminium produced accounting for ~20% of the industry average emissions. These direct emissions cannot currently be viably eliminated from the process.

 

Anode of the Future

Primary aluminium produced without carbon dioxide production at the anode is the holy grail of low carbon ‘green’ aluminium. While power can be sourced from renewable or low emission sources, lowering scope 2 emissions, there is currently no commercially viable replacement for the carbon anode   Elysis, a JV between Rio Tinto and Alcoa is developing carbon-free reduction technology which has the potential to eliminate direct carbon dioxide emissions from the reduction process. Rusal which has also invested heavily in research for an inert-anode, though in current practice still operate out-dated Soderberg anodes which are the least carbon-efficient anode. Though the company has worked to improve this with its eco-Soderberg upgrade.

Current aluminium reduction technology is also inefficient with the electricity it does consume, with estimates of up to 50% of incoming energy lost as heat. Improved refractories in cells, capable of withstanding the corrosive conditions, could also help insulate the process, keeping more heat in. Alternate anodes reducing resistance losses and improved process control are also being investigated with the aim of reducing electricity requirements and therefore Scope 2 emissions per tonne of metal production.

 

Implications?

Increasing demand from end consumers for responsibly sourced feedstocks will provide growing demand for low-carbon aluminium, though may need to expect paying a premium for it. With many producers along the aluminium value chain looking for certification by the Aluminium Stewardship Initiative (ASI) to flex their CSR credentials demand interest in low carbon products is expected to grow. Already—off a small base—primary aluminium producers are anticipating significant increases in demand for ‘green’ or low carbon metal. Norsk Hydro has stated its expectation of a more than doubling of demand for its low carbon products over 2020, with further increases forecast over 2021. While overall global aluminium demand remains largely stagnant, the company found that property developers in Europe, North America and elsewhere are increasingly willing to pay more for metal that can help to lower their carbon footprint.