Doctor of Philosophy
School of Mechanical, Materials & Mechatronic Engineering
George, Hazem Labib, Liquid flow through a reactive packed bed, Doctor of Philosophy thesis, School of Mechanical, Materials & Mechatronic Engineering, University of Wollongong, 2013. http://ro.uow.edu.au/theses/3927
The flow phenomena of liquid iron and slag in the lower zone of an iron making blast furnace influences the permeability of the coke bed, the time, and the contact area between the liquid, solid, and gas phases in this zone.
Due to the harsh environment and limited access to the lower zone of the blast furnace, several experimental simulations were conducted at room temperature, and numerical modelling studies based on these results were undertaken. While this approach gives a valuable insight into understanding the flow phenomena in this zone, it also has fundamental differences between the high temperature flow phenomena through a reactive packed bed and experiments conducted at room temperature experiments.
Limited experimental flow studies were carried out at high temperature by utilising the liquid slag and iron flowing through the coke beds. However, the limitations of high temperature experiments in a laboratory, and the heterogeneity of the metallurgical coke placed obstacles to reach a steady state of flow and made it difficult to evaluate the effect of the chemical reactions involved and to extend the variables tested.
In this project three experimental techniques were adopted and linked together in an integrated approach to study the flow of slags in the lower zone of a blast furnace passing through packed beds of coke. The slag was synthesised in compositions of a CaO-SiO2-MgO-Al2O3 system. A synthetic coke (coke analogue) was the primary packing material used to minimise the experimental uncertainty associated with the use of variable industrial coke, and to control of the mineralogy of the coke. Industrial coke was also tested as a comparison.
The flow of slag was studied on the single pore level first. The flow through pore necks that connects multiple pores in the network of pores in a packed bed was simulated by studying the flow of through a single coke channel. That was carried out by studying the flow of liquid slag at 1500°C through coke channels of variable diameters. It was found that there is a minimum channel diameter needed for the slag to enter the channel.
A simplified force balance approach based on the classical Young (1805) equation for flow through capillaries was applied to describe the flow. Applying the experimental data to this equation showed a good match to the experimental results for the non-wetting systems. This suggests that the flow is predominantly governed by gravity and the capillary forces. The results also showed a time-dependency of the flow where in some slag-coke systems the slag could flow through narrower channels when the time for the experiment was extended.
SEM and EDS analysis of the interface between the slag and coke revealed the phenomenon of Si enrichments in areas in the slag along the interface. A detailed analysis of the slag at the interface and at the bulk indicated that this Si enrichment is a result of an interfacial chemical reaction between the coke and the slag.
Secondly, to study the time dependency of the slag flow, a series of dynamic wetting measurements for the tested systems were carried out using sessile drop techniques to measure the contact angles of the slag/coke under experimental conditions. There was a dynamic wetting behaviour for most of the slag-coke systems.
Thirdly, experiments conducted with liquid slag flowing through a packed bed utilising a selection of the slags and cokes used earlier have been carried out. The flow pattern, the liquid holdup, and the liquid residence time were characterised for a number of variables. The effect of coke mineralogy, bed packing density and temperature could be tested and analysed. Furthermore, the effect of bed irrigation was tested by pre-irrigating the coke bed with slag before the experiment. The image analysis for selected sliced beds post experiment provided information about bed pore size, pore neck size and the distribution of the static holdup.
The liquid holdup and liquid residence time was found to be dependent on the packing density, the slag-coke wetting angle, the temperature and pre-irrigation of the bed. These finding generally agreed with the fundamental definitions of static and dynamic holdup, and the general trends of the mathematical formulas of static and dynamic holdup that have been based on cold experiments from the literature.
The experimental data from the liquid holdup were used to test some of the available mathematical formulae that were based on the experiment conducted at room temperature. The predicted formulae did not show an adequate match to the experimental results. A simple spread sheet iteration technique was used to modify the existing mathematical formulae to best fit the experimental results. The modified formulae were applied to the results of the high temperature experiments taken from the literature and showed a broad agreement with the experimental results.