Decarbonising blast furnace gas with chemical looping using low oxygen potential ferrites: process and thermodynamic analysis

Abstract

Previous work demonstrated Ca₂Fe₂O₅ (C₂F) can react in a blast furnace gas (BFG) with $P_{\text{CO}}/P_{C{O}_2}$ ratio of ∼1, despite of its reduction to CaO + Fe requiring a ratio of ∼3. This is possible due to the interaction with carbonation and the formation of other iron containing phases. Here, the proposed calcium and chemical looping combustion using C₂F was examined using process modelling in ASPEN Plus and MTDATA. The low chemical potential of oxygen in C₂F allows CO/H₂ combustion to be endothermic in the lower temperature carbonator (particularly when reducing to Fe_xO), leading to a more exothermic reaction during oxidation in the higher temperature calciner. In this scheme, the heat of BFG combustion is chemically pumped from the lower temperature carbonator to the higher temperature calciner using the looping material, reducing the energy use in the calciner by around 40 kW/mol-BFG compared to the calcium looping alone or to the calcium copper looping. The reincorporation of CaO and Fe/Fe_xO into C₂F would allow the calcination temperature to be lowered to 770 °C (compared with calcium looping, which requires ∼ 900 °C), and the system can be entirely autothermal.