Interactions between the process and the lining in a silicon furnace - Modelling placments of thermocouples

Abstract

The aim of this thesis is to investigate the interactions between the process and the lining in a silicon furnace. During operation of a silicon furnace incidents may occur that leads to the bottom of the furnace lining having a spike in temperature. In this paper two such incidences are found and studied. By the help of the simulating tool COMSOL ® the chain of events both on the top and inside the lining are modelled. The result of the simulations was a better understanding of what is occurring inside the furnace in such incidents, and when. After a sudden temperature increase at the top of lining the heat front uses a long time from the top to the bottom of the lining. The simulations show that the delay time from the top to the bottom of the lining varied between 18 and 23 hours. The long delay reduces the probability that a sudden severe lining problem will be discovered and corrected. The information from the thermocouples may be strongly improved by installing thermocouples higher up in the lining. This will lower the reaction time and give indication of the heat flow in the lining, as in the simulations. In addition, it was discovered that the needed temperature rise inside of the furnace to create the temperature curve of the bottom furnace lining was 250 °C, or between 400 450 °C, depending on assumptions made of the changes a furnace lining may have experienced in its lifetime. Possible explanations of two cases sudden temperature increase have been presented and discussed. Where it seems that the most likely explanation is the reduction of an endothermic reaction occurring underneath the electrode. Other possible explanations like increased heat transfer to the lining or increased heat transfer in the lining was also discussed. An even more likely explanation is a combination of two or more ex the above mentioned theories.