Experimental and Numerical Studies of Burden Layers at Blast Furnace Charging

The blast furnace (BF) is the main production unit in the processing of iron ore to molten iron (“hot metal”) in the steelmaking industry. It is a large process with huge throughput and energy consumption, so even a slight improvement of its efficiency can lead to considerable reductions in costs and harmful emissions. The charging system is the only way by which the initial distribution of the raw materials can be controlled. This distribution not only determines the structure of the arising burden bed, but also the chemical and thermal efficiency of the gas. These are crucial factors for achieving a low rate of reductants, a long life length and a more sustainable operation of the furnace.
Focusing on the behavior of particles forming heaps and layers in granular systems, this thesis has studied some questions related to burden-layer formation, burden bed properties, burden descent and gas flow distribution in the blast furnace throat and shaft.
Firstly, the effects of particle shape and physical parameters on the porosity and angle of repose of iron ore particle heaps were simulated by discrete element method (DEM). Models of non-spherical particles (cylinders and cones) were established using the sphere-cluster method. For comparison and model validation, small-scale experiments were undertaken with particles of the same shapes prepared in the laboratory. The consistency of the simulated and experimental results demonstrate that the established DEM model can be used for the prediction of the porosity of a particle system.
Some key physical parameters of the main burden materials (pellets, sinter and coke) were measured and validated by experiments. The experimentally determined parameters were the Young’s modulus, Shear modulus, Poisson’s ratio, particle density, coefficient of restitution, as well as coefficients of static and rolling friction. The experimental and calculated results were found to exhibit good agreement, which confirmed that the measured DEM parameters were of sufficient accuracy to be used in simulation of the burden distribution and descent in the blast furnace.
DEM models describing the porosity distribution and radial ore-to-coke mass ratio of the burden layers in the blast furnace shaft were successfully established based on a bell-less burden charging system with 2D slot and 3D sector throat models. An experimental bell-less charging system with a scale of 1:10 compared to an industrial BF was designed and operated in a set of experiments. DEM simulations of the corresponding system showed results in general agreement with the empirical findings, validating the numerical models.
Two kinds of non-uniform descent of burden in the upper part of the blast furnace were considered in a numerical DEM-based model, where the descent rate in the furnace center is greater than the descent rate at the wall or vice versa. The results showed that the ore-to-coke ratio decreases where the burden descent rate is low and increases where the descent rate is high.
Finally, the effect of intermittent charging on the thermal and flow conditions in the upper shaft was analyzed by Computational Fluid Dynamics (CFD) combined with DEM. A model of the counter-current flow of gas and solids and the temperature of the two phases in a simplified setup was developed. The results clarified how the temperature and velocity of the ascending gas are affected by the intermittent charging.