The global steel industry uses fossil fuels to produce millions of tonnes of iron ore sinter each year. Sintering is an energy-intensive process that fuses iron ore and flux to produce material that balances a high mechanical strength at a sufficient particle size to ensure a macroporous burden in the blast furnace to enable rapid gas flow. As significant CO₂ greenhouse emissions are emitted, the defossilisation of these CO₂ emissions is vital to net-zero carbon targets. Two iterations of a new biomass–coal hybrid fuel (ecoke^®(A) and ecoke^®(B)) were compared with coke breeze and an anthracite coal using oxygen bomb calorimetry, simultaneous thermal analysis (STA) combining thermogravimetry and differential scanning calorimetry, and isoconversional kinetic modelling and pyrolysis–GCMS to study the volatile matter. The calorific values of both ecoke^®(A) and (B) were marginally higher than that of the coke breeze: 27.9 MJ/kg and 27.8 MJ/kg, respectively, compared with 26.5 MJ/kg for the coke breeze. A proximate analysis revealed both ecoke^® samples to have higher volatile matter contents (ca. 12–13%) than the coke breeze (7.4%), but less than the anthracite coal (ca. 14%). The thermogravimetric analysis of the burnout kinetics of the fuels heated up to 1000 °C, at heating rates from 5 to 25 °C/min, showed that that the coke breeze and anthracite coal had higher ignition and burnout temperatures than the ecoke^® samples. Kinetic analysis using the Freidman and Ozawa methods found that the ecoke^® samples showed comparable maximum mass loss rates to the coke breeze but lower activation energies. From these results, both ecoke^® samples have the potential to replace some of the coke breeze in the sintering process or EAF processes to help achieve net zero by offsetting up to 30% of the CO₂ emissions.

This study investigated a novel method of recovering energy from iron ore sinter using solid iron oxide heat transfer materials. Traditionally, air is passed through the sinter either in an open conveyor or a sealed vessel to recover energy. The bed materials used were a magnetite concentrate, hematite ore, goethite–hematite ore and sinter fines. A shortwave thermal camera and quartz reactor were used measure infrared radiation from the process. The thermal imaging was combined with image analysis techniques to visualise the transfer of thermal energy through the system. The results showed that energy moved rapidly through the system with peak heating rates of 18 °C/min at a lump sinter temperature of 600 °C. The ratio of heating rate to cooling rate was as high as 8.6:1.0, indicating efficient retention of energy by the bed materials. The bed composition, determined by X-ray fluorescence and X-ray diffraction was used to calculate the heat capacity based on pure material properties. The resultant energy balance determined thermal efficiency to be between 32 and 46% for the sinter fines and hematite–goethite ore, resulting in predicted fuel savings of up to 9.4kg/tonne with similar heat utilisations to the air recovery process. Thermal imaging combined with Brunauer–Emmett–Teller surface area measurements and scanning electron microscopy analysis experimentally replicated mathematical heat transfer model predictions that a smaller total pore volume resulted in less thermally resistive bed. Image analysis illustrated the breaking of the heat front between the less resistive solid and more resistive air in porous beds versus even conduction of heat through a dense bed. The oxide distribution in the bed materials impacted heat transfer, as at a lump temperature of 500 °C was controlled by hydrated oxide content whereas at 600 °C Fe₂O₃ was the more dominant driver.