2005 Volume 45 Issue 5 Pages 662-668
The equilibrium conditions for silicon transfer from ash to the liquid metal phase via SiO gas have been discussed by several authors. However, no published calculations have been found using the most modern thermodynamic models available. Since there are major differences in the results of calculations using different thermodynamic models and the models are continuously being improved, new equilibrium calculations on SiO and SiS gas formation have been performed using the recently developed models. Different ingoing compositions of coke ash, coal powder ash and blast air were used in the calculations. The compositions chosen represent blast furnace no. 3 at SSAB in Luleå, Sweden. Temperature was found to be the major factor influencing the equilibrium silicon level in the gas phase. At low temperatures (below 1600°C) the total gas pressure was also seen to influence the silicon content in the gas phase. The main reason for this is that below 1600°C, the amount of liquid slag at equilibrium increases with the total gas pressure. Liquid slag contains large amounts of silica that then can not be found in the gas phase. Higher carbon activity is usually expected to result in higher SiO gas levels in the blast furnace. The equilibrium calculations show that increased carbon activity increases the amount of silicon in the gas phase at temperatures up to about 1600°C, but that at higher temperatures SiC is formed that decreases the equilibrium silicon level in the gas phase.
