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Abstract
An ironmaking blast furnace is the main route for producing pig iron commercially, and
it has been continuously improved to optimize operation and process efficiency over the
last century, resulting in higher production rates with relatively low operating costs. In
the last decade, the most important new technology implemented in the ironmaking
blast furnace is Pulverized Coal Injection. PCI has become more and more attractive to
iron makers due to its economic and environmental benefits. Yet problems associated
with incomplete combustion of pulverized coal in the raceway during high rates of
injection have capped the full potential of this technology. Understanding the
hydrodynamics of unburnt char within the blast furnace is therefore of great importance.
Despite this, PCI research has not been directed towards understanding the interactions
between phases (particularly unburnt char and liquid iron and slag in the lower part of
the blast furnace), because of the complexity of the problem. This thesis focuses on
quantifying the hydrodynamics of gas-powder-liquid multiphase flow in moving
particles simulating blast furnace operating conditions, providing a sound basis to
improve the four-fluid flow mathematical models for blast furnace applications related
to 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 and
gas-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 simulate
pulverized coal and coke particle, respectively. From the gas-powder two-fluid flow in
moving packed bed study, solid particle movement was found to have a significant
effect on powder hold-up behaviour in a packed bed. On the basis of the experimental
results, new static and dynamic hold-up correlations, as well as the porosity function are
proposed to account for the effect of solid movement. The interaction between gas, solid
and powder phases was also investigated. Incorporation of the proposed powder hold-up
correlations and porosity function into the existed Fanning and Ergun equations was
found to give very good predictions. As well, several gas-powder flow regimes in the
packed bed have been identified and a new technique for quantifying the powder
transport 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 this
thesis. The results indicate that steady-state gas-powder-liquid three-phase flow m
moving particles can be achieved under certain flow conditions, giving rise to
"operational" and "non-operational" regimes. The steady state condition or operational
regime, for four-fluid flow, is primarily due to the downward movement of the packed
particles which provides a higher porosity, enhances powder and liquid flow and
removes the accumulated powder. Quantification of the hydrodynamics i.e. powder
hold-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 been
studied experimentally. On the basis of these results empirical correlations for powder
hold-up and pressure drop are proposed in dimensionless form for the purpose of blast
furnace modelling.