Combined Experimental and Numerical Study of Charcoal Injection in a Blast Furnace: Effect of Biomass Pretreatment

Abstract

Carbonization is a pretreatment process for upgrading biomass to the so-called biochar or charcoal. Charcoal is a suitable alternative to coal in many fossil-based industries, especially carbon-based industries, for example, ironmaking blast furnaces (BFs). In this study, a combined experimental and numerical method is used to investigate the influence of biomass pretreatment schemes on charcoal combustion within a commercial BF. One woody biomass is upgraded to several types of charcoals using several different carbonization temperatures. The charcoal products are characterized and subjected to non-isothermal devolatilization analysis, with their kinetics calculated. The experiments indicated that the carbonization at a lower temperature produces charcoals with a higher pore fraction, larger volatile matter content, and faster devolatilization kinetics. The properties of different charcoals and their kinetic parameters are then applied to an improved three-dimensional computational fluid dynamics model for comparing the thermochemical performance of charcoal injection in the raceway cavity of an industrial-scale BF, to understand the response of the charcoal performance in the BF to the carbonization temperature. It is found out that the charcoals by carbonization at a lower temperature give higher burnouts in the raceway, but it leads to a lower gas temperature along the boundary of the raceway because of the endothermic reaction of coke and the less char combustion. The volume-averaged gas temperature within the raceway is affected by the collected results of the calorific value and burnout of charcoals. This combined experimental and modeling study discovers the impact of the biomass carbonization temperature on charcoal combustion under industrial BF conditions and can be used for charcoal design and pulverized coal injection operation optimization in future applications.