A combined experimental and numerical approach to a discrete description of indirect reduction of iron oxide

摘要

Blast furnaces are complex counter-current reactors designed to reduce chemically iron oxides and melt them to liquid iron. The complex processes in blast furnace iron making involve various aspects of thermodynamics, fluid dynamics, chemistry and physics. Physical, thermal and chemical phenomena occurring within the process are highly coupled in time and space. In order to generate a more detailed understanding of the indirect reduction of iron ore, the innovative approach of the Extended Discrete Element Method (XDEM) is applied. It describes the ore particle as discrete entities for which the thermodynamic state e.g. temperature and reduction degree through a reaction mechanism is described individually for each particle. The flow within the void space between the particles is represented by classical computational fluid dynamics that solves for the flow and temperature distribution including the composition of the gas phase. Ore particles and gas phase are tightly coupled by heat and mass transfer, that allows particles to heat up and to be provided with the reducing agent i.e. carbon monoxide. Reduction of iron oxide is predicted by a set of equilibrium reactions that represent the phase diagram of iron oxides at different oxidation levels. The reaction mechanism was validated by experimental data for a single ore particle for different temperatures. A comparison between measurements and predictions yielded good agreement so that reduction of iron oxide to iron was represented by a single mechanism including all reduction steps. The validated reaction mechanism was then applied to each particle of a packed bed that was exposed to define gas flow with its temperature and composition. The predicted results were also compared to experimental data and very good agreement was achieved. Due to the resolution of iron reduction on a particle level, detailed results of the entire reactor were obtained unveiling the underlying physics of the entire process. Results showed the reduction state of each particle during the entire period and additionally revealed the inhibiting influence of a non-uniform flow distribution. It provided regions of the packed bed with insufficient amounts of the reducing agent and thus, allowed identifying drawbacks for design and operation.