Decarbonisation Technology - November 2022

Carbon

Carbon free

Near-term (~2030) Pellets replacing sinter

Mid-term (~2040)

Long-term (~2050)

Full use of hydrogen as a reductant Hot end at renewable energy supply, cold end at market Green steel is the norm

Carbon capture Low-carbon fuels

More charge of scrap and DRI Increased energy efficiency Use of hydrogen as a fuel Carbon footp r int certificates

Partial use of hydrogen as a reductant Low carbon footprint steel is the norm

The pace will be dierent in dierent parts of the world. Viable supply of renewable power might be more pace-determining than technology

Figure 1 Neat-term activities, multiple solutions, long-term development projects

emissions due to their high CO₂ intensity of 2.3 t CO₂ per tonne of steel produced (Scope 1-3). In contrast, so-called mini-mills using the electric arc furnace (EAF) process, with recycled steel scrap as the primary feedstock, account for the balance at 30% of global steel production but produce only 10% of emissions, since they emit 0.6 t CO₂ per tonne of steel produced. While mini-mills have the potential to eliminate almost all their CO₂ emissions by using renewable electric power and green hydrogen in their existing production plants, integrated mills cannot – the blast furnace in an integrated mill requires a certain minimum level of coke (practically around 300 kg/t) to operate, with attendant CO₂ emissions from its use. Therefore, integrated mills either need ways to capture and sequester all their CO₂ emissions, or they require a fundamental change to the processing route away from the blast furnace, with concomitant Capex and Opex implications. Blast furnaces use oxygen enrichment of the cold blast to improve productivity and to enable the use of injectants through the tuyeres that reduce CO₂ emissions. Many blast furnaces operate with up to 30% oxygen in the blast today. In addition to the cold blast, oxygen can also be used in blast furnace stoves, which is a short-term way to increase energy efficiency. Stove oxygen enrichment (SOE) is a method to add high-purity oxygen to the stove combustion air to eliminate the use of sweetening high-value fuels like natural gas or coke oven gas, raise blast temperature, and debottleneck plugged stoves. Evaluations show that a 100ºC increase in blast temperature translates into coke savings of 8-12 kg/t of pig iron, with an attendant reduction in CO₂ emissions. Linde has successfully implemented

SOE in 14 blast furnaces in the Americas, Asia, and Europe. In the short term, charging of DRI, and potentially also scrap, into the blast furnace could also decrease its CO₂ emissions. While DRI is mostly charged into EAFs, it can also be briquetted into hot briquetted iron (HBI) and charged into blast furnaces or steelmaking converters to achieve decarbonisation in an integrated steel mill. As a rule of thumb, each 10% increase in burden metallisation in a blast furnace by the addition of HBI increases the production rate by 8% and decreases the coke rate by 7%, with attendant CO₂ savings. Moreover, top gas recycling of the blast furnace gas combined with carbon capture use and sequestration (CCUS) is one potential approach to reduce emissions from integrated steel mills. It is being considered at sites where CCUS is a viable option. Low-carbon fuels While hydrogen is generally considered the ultimate low- or zero-carbon fuel of the future, there are other approaches to low-carbon fuels in the near term with feedstocks derived from biomass, waste plastics, municipal solid waste (MSW), and so on. The coke rate in blast furnaces can be lowered using injectants through the tuyeres with a lower carbon footprint, such as pulverised coal, natural gas, coke oven gas, and potentially hydrogen in the future. For example, every ton of injected coal avoids 0.85-0.95 tonne of coke production, with accompanying energy savings of around 3.75 GJ/t injected coal. However, tuyere injection has its limits due to a negative impact on the Raceway Adiabatic Flame Temperature and the ability to combust