Applications of Hydrochar and Charcoal in the Iron and Steelmaking Industry—Part 2: Carburization of Liquid Iron by Addition of Iron–Carbon Briquettes

Hydrochar (a solid product from hydrothermal carbonization of organic feedstock) and charcoal have the potential to substitute coke and coal consumption in the iron and steelmaking processes for reduction of greenhouse gas (GHG) emissions. Among steelmaking processes, melt carburization is an important but less-studied application. In this study, briquettes produced with mixture a of iron powder, hydrochar or charcoal powder, and binder were tested as iron melt recarburizers. It was found that the hydrochar briquettes have good mechanical properties, whereas those of charcoal briquettes were poor. Melt carburization with briquettes was performed in a lab induction furnace (10 kg) in two steps: firstly, by heating up some briquettes with charged electrolytic iron from room temperature up to 1600 °C, followed by the addition of some briquettes into the melt. Recarburization efficiency (RE) during the first step of carburization was found to be controlled by the amount of carbon content bound in the solid phase (fixed carbon) determined at 1200 °C. Thus, the REs of charcoal briquettes (70–72%) were higher than those of hydrochar (43–58%) due to the higher fixed carbon contents in charcoal. REs obtained from the second step were strongly affected by the amount of briquette losses during their addition into the iron melt, which correlate with the mechanical strengths of the briquettes. Thus, the REs for hydrochar briquettes (48–54%) were higher than those of charcoal (26–39%). This study proves the feasibility of using hydrochar and charcoal as liquid steel recarburizers.