Means of utilising low quality high phosphorus ores and coals is the focus of much research within the steelmaking industry due to the high cost and decreasing availability of premium quality raw materials. Practices such as double converter practice are used in some steel plants to drive HM phosphorus levels down to low levels, but even then costs and time constraints are associated with such practice. To tackle this issue, a HM dephosphorisation pre-treatment process was proposed by Tata Steel R&D featuring the refinement of desulphurised HM droplets.
To determine the feasibility of dephosphorisation reaction occurring within the HM droplets as it descended down the reactor, kinetic experiments were conducted using a purpose built levitation melting furnace featuring electromagnetic coils for melting the sample. Experiments conducted included free fall and stationary levitation kinetic experiments where oxidising gas mixture and/or slag-making material was introduced into the reaction system and quenched samples were analysed for change in composition and surface morphology.
Results indicated whilst no dephosphorisation took place within the short fall time (~0.32 seconds) or during the extended reaction time (60 seconds), liquid surface oxides formed as oxidation of carbon, silicon, manganese and iron occurred. Shifted focus onto analysing the composition and growth of the surface oxides with respect to parameters such as droplet size and gas phase oxygen content showed that such factors had limited effect on oxide growth and composition. Whilst lime was unable to flux into the liquid oxide, low liquidus basic synthetic slag was able to but with no change in HM phosphorus levels. HM silicon and manganese content were however significantly lowered in the presence of the basic slag indicating mass transfer of these elements from the metal to the slag.
Whilst the significance of the experimental results is that the suggestion of extensive dephosphorisation occurring during the fall of desulphurised HM droplets within the pre-treatment process has been disproved, the study improves understanding of droplet steelmaking reactions as well as offering a new experimental technique not previously available to Tata Steel for investigating reactivity or surface properties of metal droplets.
