Combined blowing with three-hole lance in a sidewall blowing converter

Abstract

Traditionally, in stainless steelmaking converters, oxygen has been blown by a one-hole lance (1 HL) and sidewall tuyères. In order to reduce the tap-to-tap time, the multi-hole lance has been used for oxygen blowing. The aim of this work was to develop blowing practise for a multi-hole lance to reduce the tap-to-tap time and minimise metal splashing and spitting in the sidewall blowing converter (chromium converter). In the chromium converter the chemical energy of liquid ferrochrome (which contains 4% silicon and 7% carbon) is utilised for scrap melting by oxidising the silicon and the part of carbon. The research has been made by a dynamically scaled water model and full-scale converter. Used parameters were the gas flowrate from sidewall tuyères and lance, lance height, charge weight and position of multi-hole lance. Splashing has been measured during blowing from walls (splashing) and mouth of the converter model (spitting). The model tests indicated less splashing and spitting by the three-hole lance (3 HL) than traditional 1 HL. The 1 HL caused strong skulling of the converter cone. By 3 HL blowing the position of the lance has a remarkable effect on the direction and the amount of splashing and lance life. Because of hot metal-slag splashes, the life time of the 3 HL was halved by position 1 (compared to 1 HL). With the lance position 2 the splashing decreased by approx. 50% in model tests and lance life time increased by ∼ 50% (compared to 1 HL) in the full-scale converter. The model agreed well with the full-scale converter. According to the process tests, the nominal productivity of the chromium converter has increased 15% and depending on the refining practise and the silicon content of ferrochromium the lining life has increased 20 - 30%. In the future the multi-hole lance will be tested in the AOD vessel.