CO and H₂ content of the top gas has a potential to act as reducing gas elements, and therefore their recirculation to the furnace is considered as an effective alternative to improve the blast furnace performance, enhance the utilization of carbon and hydrogen, and reduce the emission of carbon oxides. In Top Gas Recycling Blast Furnace (TGRBF), oxygen is blown into the blast furnace instead of hot air to eliminate N₂ in off-gas. Part of the off-gas containing CO and H₂ is utilized again as the reducing agent in BF. CO2 from the off-gas is captured and sebsequently stored.Various recycling processes have been suggested, evaluated or practically applied for different objectives. These processes are distinguished by: 1) with or without CO₂ removal, 2) with or without preheating, and 3) the position of injection. This technology has not yet been commercially deployed, but is the focus of intensive R&D in the ULCOS program.