Towards Carbon-Neutral Ironmaking: Stepwise Integration of Biocarbon in PCI with Combustion Behavior Characterization and Injection Limit Evaluation

As the steel industry is intended to be carbon-neutral, transitional solutions are required before full-scale hydrogen-based reduction becomes viable. One such strategy is the partial replacement of pulverized coal injection (PCI) with high-quality biocarbon in blast furnace (BF) operations. Raw biomass presents challenges, such as low grindability, high ash content, and low energy density, which can be mitigated through torrefaction and carbonization. This study evaluates the combustion behavior and injection limits of four biocarbon samples (mildly torrefied biomass (MTB), hard torrefied biomass (HTB), mildly carbonized biomass (MCB), and hard carbonized biomass (HCB)) using thermogravimetric analysis (TGA), drop tube furnace (DTF), and laminar flow reactor (LFR) experiments. Results show that as biomass is carbonized, its combustion kinetics increasingly resemble those of PCI coal. Co-firing tests confirmed improved performance at higher blending ratios, especially with highly treated samples, such as HCB, due to enhanced fragmentation and char reactivity. Injection limits were determined based on combustion performance, heating value (±5% of PCI coal), and ash content (< 10%). The MTB and HCB exceeded these limits at approximately 27%–30% blending, indicating the need for an adjusted fuel input. Overall, biocarbon shows strong potential as a PCI substitute, offering a feasible low-carbon pathway for existing BF systems.