Study On Formation Mechanism Of Blast Furnace Hearth Sediment Of High Alumina And Titanium

BF is a major smelting vanadium-titanium magnetite of the Chengde Iron and Steel Company. A lot of sediments were found in blast furnace hearth, while blast furnace was overhauled. The sediments are in the bottom of the pot-shaped, which has seriously affected the normal production of blast furnace. Therefore formation of hearth sediment is studied in this paper.The composition and nature of the sediment are studied initially. The results show that, sediments are wrapped with metallic luster iron. It's black and with high hardness .In the furnace of molybdenum silicide, at 1600℃, the sediment becomes soft but not melting. High melting temperature materials in the sediments are mainly spinel and TiC, TiN and Ti (N, C) and Ti (C, N). TiC mainly distributes in the surrounding iron, while Ti (C, N) and Ti (N, C) are scattered or reunited in compound of spinel and rutile.Sediment layers can be divided into molten iron layer, titanium sedimentary deposit, and transition erosion layer. Molten iron layer contains high contents metal iron. Titanium sedimentary deposit mainly contains MgAl2O4, TiC, TiN and their solid solutions. The main components of the transition erosion layer are refractories eroded by hot metal and slag. From the top down, the silicon contents gradually increase while the titanium and ferrous contents gradually decrease.Through studing on smelting magnetite in the blast furnace and the formation of TiC, TiN and Ti (C, N), the formation of sediments can be obtained as follows: direct reduction takes place between Titanium in slag and coke with TiC generating. TiC in slag is absorbed by hot iron drop, then bundles surrounding hot iron drop. TiC which bundles surrounding hot iron drop settles to the BF bottom and forms the sediments. In the iron- slag and iron-refractory interface, due to the existence of concentration gradient and temperature precipitation gradient, Ti (N, C) is separating out and settlement, deposit in the hearth form hearth sediments.The main reason of sediment formation is that there are a large number of coke and aluminum in slag. It makes the slag viscosity increase and reduce the mobility of the slag. Then slag with high melting temperature material accumulation in the bottom forms sediments. Through experiments, slag alkalinity of BF should be controlled around 1.02, not to exceed 1.22. MgO content of the slag should be chosen in the average of 11.95% ~13.95%. By pyrolusite prepurging, melting temperature of the sediment can be reduced and even some of the sediment can be eliminated.