Mathematical modelling of gas-solid flow and thermal behaviour in an ironmaking blast furnace

摘要

The ironmaking blast furnace (BF) remains the most significant and important process for the production of liquid iron. For the achievement of stable furnace operation and good performance, mathematical modellings at different levels increasingly become a powerful tool in developing better understanding of this multiphase flow system, in particular the gas-solid flow. This thesis represents an effort in this area.A simplified and continuum-based mathematical model is proposed and tested to predictthe BF gas-solid flow at a macroscopic level. The results show that the simple model isable to predict the general features of the solid flow, including the effects of gas andsolid flowrates, and materials properties. The simplified model can be readilyimplemented in a full process model that needs to have a quick response to change forthe purpose of control and optimization.To overcome the difficulties encountered in continuum modelling, i.e. determination ofconstitutive correlations, and particularly the description of the stagnant zone whenrelated to BF, a discrete model based on the coupling approach of discrete elementmethod (DEM) and computational fluid dynamics (CFD) is then employed toinvestigate the gas-solid flow in a model BF at a microscopic level. The results confirmthe effects of variables such as gas flow rate, solid flow rate, particle properties, andmodel types. More importantly, such an approach can generate abundant microscopicinformation such as flow structure (particle velocity, porosity, coordination number) andforce structure, which are of paramount importance to elucidate the gas-solid flowmechanisms, and develop a more comprehensive understanding of BF gas-solid flow,such as the formation mechanism of the stagnant zone. Further, the transient gas-solidflow phenomena, together with the considerations of cohesive zones and hearth liquid,can be predicted.Further, in order to develop understanding of thermal behaviour and elucidate the heattransfer mechanisms occurring in particle-fluid flow system, a new model is proposedby extending the DEM-CFD, and then tested in gas fluidization. The model considersthe three heat transfer modes, and demonstrates its ability in investigating the heattransfer mechanisms, and offers an effective method to elucidate the mechanisms governing the heat transfer in particle-fluid systems at a particle scale. It isrecommended to apply to the study of BF thermal behaviour.