Relaunching a process that uses 100% H2 for the direct reduction of iron ore

Developed two decades ago, Metso Outotec’s (MO; Helsinki, Finland; www.mogroup.com) Circored process is now being reintroduced as a proven way to help decarbonize the ironmaking process. Developed in the 1990s by the former Lurgi Metallurgie (now part of MO) and continually refined, Circored is a hydrogen-based process for the direct reduction of iron-ore fines to produce zero-carbon hot-briquetted iron (HBI) or direct-reduced iron (DRI), which is used in electric-arc furnaces (EAFs) for steelmaking. Circored uses 100% H₂ as the reducing agent, which enables low-temperature operation (below 650°C) and avoids sticking problems associated with alternative DRI processes, says Sebastian Lang, director for Modeling & New Business of the Ferrous & Heat Transfer business line at MO. The process also operates at higher pressure (4 bars), which allows a reduction in equipment and piping sizes, thereby lowering capital expenditures (capex), he says.

Circored is a two-stage reduction system consisting of a circulating fluidized-bed (CFB) reactor, in which the reaction is controlled by interfacial mass transfer, and a bubbling fluidized-bed (FB) reactor, in which the reduction reaction is diffusion controlled (diagram, right; and flowsheet, below). Ultimately, more than 93% metallization degree is achieved. Circored does not require a pelletizing plant, which is used to prepare iron ore for feeding a blast furnace (to make pig iron) or a shaft furnace (alternate route to DRI/HBI). Also, the metallurgical coke (from coal) used in blast furnaces is eliminated. As a result, CO₂ emissions for Circored — operating with H₂ produced from conventional steam-methane reforming (SMR) as the H₂ source, for example — are about half that generated by traditional blast furnace routes. If “green H₂ ” is used as reductant and electric energy for process gas heating — dubbed Circored+ — CO₂ emissions are essentially zero. However, the Circored Process is neutral to the origin of H₂.

Circored has already been proven at industrial scale, having been used in a demonstration plant in Point Lisas, Trinidad (Chem. Eng., September 1996, p. 25). The plant operated from 1999 to 2005, producing 500,000 ton/yr of HBI. “If you asked me, this plant was erected 20 years too early,” says Lang. “Today, the market drivers have dramatically changed, and direct reduction based on H₂ makes more sense than ever before as a solution to decarbonize the steel industry.”