Dynamic end-point control in BOF through a fast and simultaneous determination of the steel/slag composition (Bofdyn) : final report

In order to achieve shorter tap-to-tap time and hence higher productivity at the BOF, process events related to the control of the melt analysis, such as stop of the oxygen blow, lance withdrawal or vessel tilting, have to be avoided. A new method for controlling the BOF process is proposed here. It involves the use of an original in-blow heterogeneous sampler simultaneously collecting slag and steel and a dedicated laser analytical method (LIBS). With this method, the aim is to deliver as quickly as possible a complete analysis of the steel and slag collected by the heterogeneous sampler (Fe, C, P, S ...). Besides the setting-up of the heterogeneous in-line sampling, a specific procedure has been developed in order to recognise the laser shots coming out from slag and from steel when moving the heterogeneous sample during its analysis. Combined with a metallurgical model, the processing of the data generated with the heterogeneous sampler leads to dynamically assess the state of the refining progress and to define the corrective actions in order to allow a safe direct tapping practice. The expected benefits are a reduced reblow rate, a tap-to-tap saving (a gain of 2-3 minutes per heat can be expected), a reduced trunion wear, as well as an increased refractory lining life and process yield. Developed for a converter without sub-lance, the method was adapted for converters equipped with a sub-lance. Results of orientation tests are presented here.