Calix technology for zero emissions iron and steel ZESTY

Iron and steel production is the second largest source of man-made industrial CO₂ emissions, responsible for an estimated 2.6 billion tonnes per year, or approximately 7%* of global industrial emissions. Mitigating CO₂ emissions from the iron and steel industry will be critical to ensuring we can simultaneously meet our goals for social, economic and environmental sustainability.

The challenge

Between 80 and 85% of the industry’s CO₂ footprint is linked with the production of iron, as 90% of all iron is produced by metallurgical coal- and coke-fuelled blast furnaces, producing nearly 1.8 tonnes of CO₂ per tonne of iron produced.

Iron produced via direct reduction of iron ore using a ‘syngas’ of hydrogen and carbon monoxide (made from natural gas) in a shaft furnace is a less CO₂-intensive method, at around 0.6 tonnes of CO₂ per tonne of iron; however, this process route has traditionally been more expensive, and hence only 10% of the world’s iron is produced by this method. The method requires cheap natural gas, as well as pelletisation of iron ores to prevent fines loss.

Methods to lower the carbon footprint of iron production have started to consider using green hydrogen as the major reductant instead of natural gas and coal. The use of hydrogen in blast furnaces is being tested, but there are limits on the amount of coal it could replace due to a reduction in the conversion rate of iron ore to iron.

Our solution

Calix’s ZESTY uses green hydrogen in a renewably powered reactor to produce green iron and ultimately, green steel.

ZESTY’s unique, indirect heating approach not only enables efficient electrification, but means hydrogen is not consumed as a fuel, only a reductant, and is easily recycled in the process. This significantly lowers operating temperatures and potentially enables the most efficient and economical use possible of hydrogen.

ZESTY’s ability to handle small particle sizes has the potential to more easily remove impurities compared with other direct reduced iron (DRI) processes, which require pelletised and typically higher grade iron ores.

The ZESTY process produces green iron from multiple ore types for use in either conventional blast furnaces for lower carbon steel products or directly in electric arc furnaces (EAF) for zero emissions steel.the The ZESTY Steel process uses zero emissions lime produced by a Leilac kiln, while the lime can also scrub excess carbon dioxide as well as other pollutants from the exhaust gases.

ZESTY features:

• Hydrogen reduction of iron ore;
• Can be easily and efficiently renewably powered;
• Targeting theoretical minimum hydrogen use;
• Compatible with multiple ore types;
• Processes fines

_{Source: Climate change and the production of iron and steel. World Steel Association. 2021}

1. Iron ore is inserted into the top of the ZESTY reactor where it is exposed to preheated green hydrogen.

2. The hydrogen strips the oxygen from the iron ore, producing metallic iron (sponge iron or Direct Reduced Iron) and steam.

3. The carbon free ZESTY process uses renewable electricity and a heat recovery steam generator to power the reactor, electrolyser and electric arc furnace.

4. Direct Reduced Iron is hot discharged into the electric arc furnace to produce green steel with zero CO2 emissions. A heat recovery generator converts energy from the hot exhaust gas back into electricity.

5. Excess hydrogen is recycled back to the ZESTY reactor. Steam produced by the reactor is condensed and then split by the electrolyser, producing hydrogen for the reactor and oxygen for the electric arc furnace.