ESiP - Energy efficient Silicon Production

The ESiP project goal is to obtain at least 5 % more energy efficient silicon production by developing and applying operating support systems for silicon furnace operation. In today's operation, silicon yields around 80 % are typical, meaning that 20 % of the silicon is lost in the off gas from the furnace. To operate a furnace at higher silicon yield, we have to identify and quantify the parameters affecting the chemical reactions, by implementing new measurement techniques and apply the new information in operation support systems. The development of the operating support system has been organized in three major activities: 1) Increase the process information from a silicon furnace charge surface by implementing new systems for measuring surface temperatures and charge mix topography. In 2014, a thermo-camera was successfully installed at an industrial silicon furnace. This camera can see through the flames at the furnace surface and has given new insight of the surface conditions in the furnace. The new camera was highly embraced by the furnace operators. In November 2015 and November 2016, camera systems were installed at two new furnaces, so that there are now three camera systems in operation as direct results of the project. 2) High temperature lab studies are important for investigation of the reaction mechanisms in the silicon process. High-temperature properties of quartz have been the main topic in 2014-15. This work has resulted in new fundamental knowledge of how quartz properties affect the furnace operation. In 2015, a test program for new potential quartz materials in Elkem was developed. Moreover, chemical reactions involving SiO2 has been investigated in more than 30 lab experiments at Sintef. 3) The main part of the operating support system will be a simulation model of a silicon furnace developed from physical principles and adapted to an actual industrial furnace, incorporating the new knowledge about chemical reactions from the laboratory investigations. Key parts of the modelling work have been to exploit new information from the camera about the charge surface conditions, and a newly designed user interface with signal processing for the camera monitoring has been included in the system. At the end of 2016, the simulation model is connected on-line to the three furnaces that also have installed the camera monitoring. The operational support system is constitutes of the on-line model and the camera system with the user interface. In addition, the project has developed a prototype for a simpler operating support system that has been implemented at into several silicon furnaces.

The ESiP goal is to obtain 5% more energy efficient silicon production by developing and applying an operating support system for silicon furnace operation. Presently, a silicon yield of 80% is typical; meaning that 20% of the silicon is lost in the off g as from the furnace. Energy cost is one of the main cost elements in silicon production, accounting for around 1/3 of the overall production costs. Increasing the silicon yield from 80% to 85% will lower the specific energy consumption from around 12.0 to 11.4 MWh/t. The development of this operating support system is based on three major activities: 1) Increase the process information from a silicon furnace charge surface by implementing new systems for measuring surface temperatures, charge mix topogra phy and off gas chemical composition. 2) Performing high-temperature (>2000°C) lab-scale and pilot experiments to gain increased knowledge about material and energy flows in a silicon furnace and investigate the chemical reaction kinetics. The main resul ts will be kinetic data for process reactions, new understanding of how raw material properties affect process reactions and the coupling between reactions and energy distribution and how this will affect the silicon yield. 3) Developing an operating supp ort system based on a simulation model of a silicon furnace developed from physical principles and adapted to industrial use by continuous testing and modification on an industrial furnace in parallel with the model development. The model will use process information from the new charge surface measurements and new process knowledge gained from the experimental work. The user interface will be developed in close cooperation with process operators and engineers. By combining model information with online m easurements, improved furnace control strategies and raw material optimization, the hypothesis is that the silicon loss can be reduced considerably, resulting in a more energy efficient production of silicon.