A Fundamental Study of the Cocombustion of Coke and Charcoal during Iron Ore Sintering

In a global carbon cycle, the net greenhouse gas (e.g., CO2) emissions can be significantly reduced if fossil fuels could be substituted with renewable and cleaner biomass-derived fuels. In the traditional iron ore sintering process, the complete replacement of coke, a coal-derived fuel, with charcoal is not possible because the two fuels have very different properties and combustion behaviors, resulting in an unacceptable deterioration in sintering performance. Consequently, only low substitution ratios can be tolerated. However, research has indicated that this ratio can be increased through altering the combustion behavior of charcoal. Most fuel particles in a sintering bed have an encapsulated layer of fine ore and flux particles. Through intentionally altering the properties of this adhering layer, combustion behavior can be altered, leading to improved sintering performance. This work uses a newly developed combustion model and a 2D sintering model to appropriately describe the combustion behavior in sintering based on fuel properties and defines the optimum thickness and porosity of the adhering layer. In this study, the required properties of the adhering layer encapsulating charcoal particles, so as to match the combustion behavior of coke particles, are determined theoretically. This study also shows that the conditions required for different fuels to have similar sintering performance are (a) comparable ignition temperature and overall combustion rate, and (b) comparable rates of combustion at various temperatures. Matching the overall combustion rate alone does not necessarily result in comparable sintering performance. Meanwhile, the apparent density and water holding capacity of the substituting fuels should be close to the equivalent values for coke to ensure similar granulation performance and, subsequently, the properties of the bed prepared for sintering. Until these conditions are fully met, combustion efficiency, the properties of the formed flame front (e.g., width, temperature, and speed), and, consequently, sintering performance will deteriorate. In practice, fully matching all of these conditions is difficult. The present work has given guidelines on which are the critical variables of the adhering fines layer that have to be considered when charcoal is introduced into sintering and also how the variables interact to determine flame front properties.