CFD study of the combustion of innovative fuels in blast furnaces for sustainable iron making

Abstract

The implementation of innovative fuels is considered as an imperative and essential countermeasure for sustainable ironmaking. Biomass and hydrogen are regarded as promising renewable fuels to mitigate CO2 emission, and low-rank coal is regarded as flexible fuel to maintain the supply chain. Pulverised coal injection (PCI) technology has the readiness to accommodate these innovative fuels in ironmaking blast furnaces (BFs). However, the in-furnace phenomena of innovative fuels injection are not clear yet. In this thesis, several computational fluid dynamics (CFD) models are developed and applied to simulate the combustion of innovative fuels under real BF conditions. Firstly, a 3D CFD model is developed to simulate the flow and thermochemical behaviours of the pulverised biomass injection (PBI), and applied to pilot-scale and then industrial-scale simulations. The model features hollow cylindrical biomass particles and modified sub-models of biomass chemical reactions. It was validated against coal combustion in a commercial BF and biomass combustion in a pilot-scale PCI test rig. The key phenomena of the selected PBI were found to be comparable with two typical PCI coals. The model is finally used to investigate the influence of key PCI operation variables and biomass pretreatment schemes. Secondly, a 3D industrial-scale CFD model is developed to study the feasibility of semicoke (upgraded low-rank coal), in collaboration with lab-experiments and plant-tests. The simulation results show that, by optimisation, similar combustion profiles of semicoke with coal can be achieved. Also, the effect of the blending ratio is studied. The plant test with a blending ratio of 0–20% indicates that ironmaking indices remain stable, confirming the practical feasibility of semicoke co-injection operation. Finally, a 3D industrial-scale CFD model is developed for the co-injection of H2-PCI. The H2-PCI model features chemical reactions of hydrogen/H2O and H2-coal interactions. The model was validated based on coal injection in a commercial BF and co-injection in a pilot-scale test rig. Several injection schemes of H2-PCI were designed based on the constant bosh gas volume. The typical in-furnace phenomena and effects of blending ratios on combustion performance were investigated. The CFD models developed provides a cost-effective tool for understanding the combustion behaviour of innovative fuels and operation optimisation for sustainable ironmaking.