(p647) Present IJmuiden Limestone-Dolomite Pellets: evolution of the pellet flux

摘要

The Tata Steel IJmuiden pellet plant is part of the IJmuiden integrated steel plant. Traditionally, this pellet plantproduced acid olivine fluxed pellets. In order to lower the blast furnace slag rate, the olivine in pellets has beenreplaced by carbonate fluxes. Based on the specifications for blast furnace slag and sinter and limitations to theflux dosing in the pellet plant, a dolomite fluxed pellet was developed. The transition initially failed in December2011, as pellets caused process disturbances in the blast furnace which were related to severe pellet swelling.Dolomite pellets were reintroduced in March 2012 after extensive research on pellet induration and swelling as wellas a program in the pellet plant itself focussing on all aspects of pellet making. Dolomite pellets were madesuccessfully with a fixed lime/silica ratio of 0.75.The dolomite pellets performed well in the blast furnace. However, the blast furnace slag MgO increased tounacceptable levels of 12% since the pellet MgO was no longer a free variable, but depended on the pellet silicalevel (if lime/silica ratio was to be kept fixed). As a countermeasure, it was chosen to replace part of the dolomite bylimestone. Due to logistical limitations, premixing of limestone and dolomite has to be done outside the pellet plant.In order to meet the specifications on the lime/silica ratio this has to be done under close monitoring.Despite this change to carbonate fluxed pellets the plant productivity recovered to levels reached while producingolivine pellets. High control of blend, blaine, balling and induration conditions allowed this success. Until now theswelling of the pellets remains an issue of constant close monitoring and investigation.