Slag and its Role in Blast Furnace Ironmaking Aug07

Slag and its Role in Blast Furnace Ironmaking...

Slag and its Role in Blast Furnace Ironmaking Blast furnace (BF) is the oldest (more than 700 years old) of the various reactors which are being used in the steel plants. It is used for the production of liquid iron (hot metal). The blast furnace is a complex high temperature counter current reactor and is in the shape of a shaft in which iron bearing materials (ore, sinter/pellet) and coke are alternately charged at the top along with flux materials (limestone, dolomite etc.) to create a layered burden in the furnace. Preheated air is blown in from the lower part of the furnace through tuyeres. This hot air reacts with the coke to produce reducing gases. Descending ore burden (iron oxides) is reduced by the ascending reducing gases and is melted to produce hot metal. The gangue materials and coke ash melt to form slag with the fluxing materials. The liquid products (hot metal and slag) are drained out (tapped) from the furnace at certain intervals through the tap hole. The quality of hot metal obtained is dependent on the formation of the slag and its mineralogical transformations. A good quality slag is necessary for a quality hot metal. The slag is a mixture of low melting chemical compounds formed by the chemical reaction of the gangue of the iron bearing burden and coke ash with the flux materials in the charge. All unreduced compounds such as silicates, aluminosilicates, and calcium alumino silicate etc. also join the slag. It is well known that the components of slag namely silica (SiO2) and alumina (Al2O3) increase the viscosity whereas the presence of calcium oxide reduces the viscosity. The melting zone of slag determines the cohesive zone of blast furnace and hence the fluidity and melting characteristics...