This Report investigates the viability of biochar for decarbonising Bluescope’s Port Kembla Steelworks. It includes an overview of the current state of biochar supply in Australia, available pyrolysis technologies, and results from pilot testing in their blast furnace.
Like coal, biochar that is to be used for ironmaking requires a relatively tight specification in terms of ash, ash chemistry, heavy metal concentrations and to a lesser extent volatile matter content. Ash is important as higher proportions reduce the amount of solid carbon in the biochar and increases fuel consumption and potentially requires additional fluxes to be melted in the blast furnace. Some ash components such as phosphorus-, sulphur-, alkali- and zinc-based oxides are problematic in iron and steelmaking processes and therefore must be minimized.
Similarly, heavy metals (e.g. lead, mercury and arsenic) may be problematic for integrated steelworks due to the potential impact on environmental discharges and in extreme cases to employee health. Finally, volatile matter content might be minimized, to maximize the solid carbon reaching the blast furnace. However, given volatile matter content is dictated by pyrolysis temperature, which in turn dictates the biochar yield , there is still some question about the ideal level, from a cost and blast furnace operations perspective. This question cannot be addressed until longer duration, large-scale trials with biochars of different volatile matter content are conducted at a blast furnace. Indeed, there are significant moves to test at full scale the use of torrefied wood or bio-coal (timber subject to pyrolysis below 320oC) as a coal substitute in blast furnace applications .