SiO2-CaO-Al2O3 slags in Si/FeSi furnaces

Slag samples from five industrial Si furnaces and one FeSi furnace excavation have been investigated in this study. For one furnace, the slag close to the tapping canal was investigated more thoroughly. The furnace is divided into three main areas: higher up in the furnace, near the furnace bottom and samples from zones near the tapping canal. It is found that the slag mainly consists of different compositions of SiO2-CaO-Al2O3 and that the areas higher up in the furnaces generally contains more SiO2 than in the bottom. It is also found that the composition varies more in the higher parts of the furnaces. The second part of the study includes tapped slag from two of the Si furnaces. Slag have been collected from the tap-hole at Elkem Thamshavn regularly in a period of one year, and three slag samples are collected from Furnace B. It is found that the slag composition does not vary much over time, neither from day to day nor in monthly basis. It is also found that the tapped slag is a mix of the slag inside the furnace and is hence more affected by the accumulated furnace slag than the slag produced from the recently added raw materials.