A detailed study of the reaction of natural ilmenite in the rotary carbonaceous reduction kiln is made.
A review of literature concerning reduction kinetic testing of iron oxides is presented. The historical development of the research is outlined. The role of physical characteristics (such as iron film thickness and porosity) on gas transport processes and the subsequent reduction rate is studied. It is demonstrated that none of the kinetic studies have obtained a true chemical reaction rate for iron oxide reduction.
The similarities between the well studied, iron oxide reduction situation and the ilmenite reduction situation are indicated. The additional complexities of the ilmenite weathering process and high temperature phase chemistry are explained. The available literature of reduction studies is reviewed. It is shown that the development of a phenomenological model of reduction of ilmenite particles is not possible given the current understanding. Empirical reduction test work using the CSIRO boat test and RGCMS rotating pot test procedure is described. A generalised metallisation model is developed and applied to analysis of the experimental data. It is shown that the metallisation model results, from these test procedures, can be related to metallisation results in pilot and commercial scale reduction kilns.
Experimental results are presented investigating the role of coal type on reduction reactivity. The important role of H2, released from the coal during the charring process, is highlighted. Gas composition measurements during rotating pot test work and analysis of commercial kiln metallisation profiles suggests that H2 is an active reductant in commercial kilns.
A literature review of published work on rotary kiln modelling is presented. The important aspects of modelling commercial scale ilmenite reduction kilns are emphasised.
A description of the mechanistic dynamic rotary kiln model is given. The major model assumptions are described. A detailed explanation of the assumptions made in modelling the ilmenite reaction chemistry is presented.
Results of the steady state tuning of the model to plant conditions are presented for the smallest ('A' kiln) and largest ('D' kiln) of the RGCMS commercial ilmenite reduction kilns. It is demonstrated that reduction due to H2 is as significant as reduction due to CO in the commercial scale kiln. Many interesting insights into the physical characteristics within the commercial kilns are obtained.
The dynamic response of the model to typical changes in operating variables is tested. The importance of the operating variables in influencing the operation of the kiln is discussed. The adjustment of kiln shell tube air addition is shown to be the most sensitive operating variable. Other variables are ranked in terms of their influence on the process. The results provide insight into the transient operating characteristics of the commercial kiln.
The response of the model to transient changes in the ambient air temperature and composition of the ilmenite is tested. Typical operating data is presented and it is shown that the performance of the commercial kilns can be considerably improved by some simple control strategies and improved instrumentation. Finally, the potential of model based design studies and control strategies is examined. Aspects of the model requiring further refinement are outlined.