2.2.2. Steel

Construction steel, often galvanized, is predominantly produced by primary steel, i.e., from iron ore in integrated steel plants, while reinforcement steel is mainly produced by scrap steel in secondary steelmaking plants, called electric arc furnaces (EAF), although depending on the availability of scrap steel, this varies globally [107]. Predominant current abatement options to reduce embodied emissions associated with steel are enhanced material efficiency and circularity measures [9,15,58,108]. The main opportunities lie in reducing waste during the construction process; reduce the amount of material in each building by avoiding over-specification and using higher-strength materials; and reusing buildings and building components [38,44,109]. With better sorting and separation, there is also a potential for increased scrap share for construction steel production [38,110].

Regarding the different production methods, EAFs mainly use electricity but also require fueling by natural gas (25–30%) and a smaller share of coal (<5%) [70–73]. With electricity as the main energy carrier, the emission intensity of the electricity used is an important factor [107,108]. Refurbishments and upgrades of current electric arc furnaces provide potential for decreased electricity consumption [70,111,112], and there is also potential for biomass to substitute fossil process energy in EAFs, both as a reducing agen<sup>t</sup> and as fuel in reheating furnaces [70,73,113]. Fuel substitution from natural gas to bio-based syngas or biooil is similarly proposed in metallurgical processes [114].

For primary steel production, about 80% of the CO2 emissions stem from the reduction of iron ore [22,23,115]. The main options for deep emission reduction in primary steel production are electrification with renewable electricity (either via hydrogen direct reduction or through electrowinning) [22,26,71,90,115–117], use of biomass to replace coke as fuel and reducing agen<sup>t</sup> [26,76,113,118–122], and/or use of carbon capture and storage (CCS) [22,26,40,117,123,124]. Partial CO2 capture is a mature and low-cost technology that can be implemented in the coming 10–15 years without major changes to the existing process and which can be combined with biomass substitution [123,125,126].
