Gas-powder-liquid three-fluid flow in moving particles for blast furnace modelling

An ironmaking blast furnace is the main route for producing pig iron commercially, andit has been continuously improved to optimize operation and process efficiency over thelast century, resulting in higher production rates with relatively low operating costs. Inthe last decade, the most important new technology implemented in the ironmakingblast furnace is Pulverized Coal Injection. PCI has become more and more attractive toiron makers due to its economic and environmental benefits. Yet problems associatedwith incomplete combustion of pulverized coal in the raceway during high rates ofinjection have capped the full potential of this technology. Understanding thehydrodynamics of unburnt char within the blast furnace is therefore of great importance.Despite this, PCI research has not been directed towards understanding the interactionsbetween phases (particularly unburnt char and liquid iron and slag in the lower part ofthe blast furnace), because of the complexity of the problem. This thesis focuses onquantifying the hydrodynamics of gas-powder-liquid multiphase flow in movingparticles simulating blast furnace operating conditions, providing a sound basis toimprove the four-fluid flow mathematical models for blast furnace applications relatedto operations, and sheds more light on the problems of PCI at higher injection rates.A systematic experimental study of the hydrodynamics of gas-powder two-phase andgas-powder-liquid three-phase flows in fixed and moving packed beds was carried out.Glass and plastic powders and glass beads of various sizes were used to simulatepulverized coal and coke particle, respectively. From the gas-powder two-fluid flow inmoving packed bed study, solid particle movement was found to have a significanteffect on powder hold-up behaviour in a packed bed. On the basis of the experimentalresults, new static and dynamic hold-up correlations, as well as the porosity function areproposed to account for the effect of solid movement. The interaction between gas, solidand powder phases was also investigated. Incorporation of the proposed powder hold-upcorrelations and porosity function into the existed Fanning and Ergun equations wasfound to give very good predictions. As well, several gas-powder flow regimes in thepacked bed have been identified and a new technique for quantifying the powdertransport velocity is proposed.The study of the so-called four-fluid flow under blast furnace conditions, i.e. gas powder-liquid three-fluid flow in moving particles, is the primary objective of thisthesis. The results indicate that steady-state gas-powder-liquid three-phase flow mmoving particles can be achieved under certain flow conditions, giving rise to"operational" and "non-operational" regimes. The steady state condition or operationalregime, for four-fluid flow, is primarily due to the downward movement of the packedparticles which provides a higher porosity, enhances powder and liquid flow andremoves the accumulated powder. Quantification of the hydrodynamics i.e. powderhold-up and pressure drop of four-fluid flow is possible within the operational regime.The effect of flow variables such as gas, powder, liquid and solid flowrates has beenstudied experimentally. On the basis of these results empirical correlations for powderhold-up and pressure drop are proposed in dimensionless form for the purpose of blastfurnace modelling