structural:summarization, structural:reformatting
BOF

Top gas from the blast furnace is the gas that is normally exhausted into the air during steelmaking. This gas contains CO and is also rich in the reducing agents of H and CO. The top gas can be captured, the CO removed, and the reducing agents reinjected into the blast furnace. A 2012 study suggested that this process can reduce BF CO emissions by 75%, while a 2017 study showed that emissions are reduced by 56.5% with carbon capture and storage, and reduced by 26.2% if only the recycling of the reducing agents is used. To keep the carbon captured from entering the atmosphere, a method of storing it or using it would have to be found.

Another way to use the top gas would be in a top recovery turbine which then generates electricity, which could be used to reduce the energy intensity of the process, if electric arc smelting is used. Carbon could also be captured from gases in the coke oven. As of 2022, separating the CO2 from other gases and components in the system, and the high cost of the equipment and infrastructure changes needed, have kept this strategy minimal, but the potential for emission reduction has been estimated to be up to 65% to 80%.