D. Satish Kumar, Sundaresan S., Vasa S. N. Murthy, Prabhat K. Ghorui, and Madhu Ranjan:
Pretreatment of hot metal
Hot metal pretreatment, desiliconisation, dephosphorisation
In present times, the products of most of the iron making units are characterised by high silicon and phosphorus contents, due to poor raw material characteristics. Removal of these impurities increases the processing time at the converter and ladle treatment. Additionally, increasingly stringent quality requirements have heightened the demand for steels with very low levels of impurities, such as phosphorus, sulfur, hydrogen, nitrogen, oxygen, and of non-metallic inclusions. To improve hot metal characteristics, several attempts to pretreat the hot metal have been made on various scales by steel plants with limited success. No full-scale hot-metal pretreatment has been proved successful.
With the aim to understand the hot metal refining mechanism and establish an economically viable process, JSW Steel, Vijayanagar works, has introduced India’s first hot metal pretreatment (HMPT) facility. The HMPT envisaged the removal of silicon and phosphorus separately by injection of reagents and fluxes in the transfer ladle in a twostep process. Desiliconisation was attempted by oxidising the hot metal along with added lime and sinter fines (iron oxide) to form a CaO-FeO-SiO2 slag, whereas dephosphorisation is carried out by lime, sinter fines and fluorspar.
Series of trials were made to optimise the addition and blowing pattern for the most economical treatment in the least possible time. Successful and continuous pretreatment of hot metal has resulted in significant improvement during primary steel making, and reduced the desiliconisation and dephosphorisation load on the converter.
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