Silicon Production with use of Natural Gas

Silicon is produced in smelting furnaces with quartz (SiO2) as the silicon source, and various carbon materials such as coal, charcoal and wood chips, as reduction materials. Typically, 80% of the silicon in the quartz is recovered as tapped silicon from the furnace (Si yield), while 20% is lost as SiO2-fume in the off gas from the furnace. The objective of the SiNG project is to develop a new raw material for silicon production made from natural gas and quartz. The new material will be carbon-silica agglomerates that have the potential of partly replacing coal as reduction material in the process. Use of this new raw material has two main advantages: 1) Increased Si yield 2) Reduced specific CO2 consumption. The increased Si yield is achieved by a change in the chemical reaction patterns in the furnace. By using the new material accounting for 25% of the quartz needed, the Si yield is supposed to increase by 5%, equivalent to 5% increased energy efficiency. Use of a natural gas based raw material partly substituting coal, will reduce the CO2 emissions of silicon production, and especially emissions of fossil CO2. Use of the 25% of the new material by reducing coal, will reduce the CO2 emission by around 10%. The results from SiNG can be used applied with present silicon furnace technology. This differs from other research initiatives using natural gas as reductant on silicon production where a new process technology must be developed. SiNG is divided into work packages: 1) Investigation of how carbon-silica agglomerates for silicon production can be produced from natural gas and quartz. 2) Study of how use of these agglomerates will change the chemical reaction patterns so that increased Si yield can be achieved. 3) Laboratory investigations to verify the results and develop an industrial operational strategy for the use of this type of raw materials. The project has in 2017 mainly focused on final lab investigation of the produced SiO2-C material properties and reporting activities from the previous years. The project has only focused on laboratory investigations to understand the process phenomena before scaling up. The PhD student has finished his experimental work and his PhD thesis. He defended his PhD degree 5 October 2017. He then joined Elkem to continue his R&D work into industrial applications. A master student took his degree in WP1 in 2014-15.

SiNG will develop a new raw material for silicon (Si) and ferrosilicon (FeSi) production from natural gas and quartz. The new material will be a carbon-silica agglomerate that partly will replace coal as reduction material in the process. Use of this new agglomerate in the raw material mix will increase the Si yield for the production significantly. This is achieved by a change in the chemical reaction patterns in the furnace. By using the new material accounting for 25% of the carbon needed, the Si yield is supposed to increase from todays 80% to 85%. The increased production represent a value of more than 200 MNOK NOK/year if it is implemented on Elkem?s Norwegian furnaces. The increased Si yield will lower the specific energy consumption from around 1 2.0 MWh/t to 11.4 MWh/t for Si, equivalent to 5 % increased energy efficiency, corresponding to 110 GWh/year for Elkem in Norway. This will reduce the production cost by 2 %; approximately 200 NOK/t. Elkems annual silicon production in Norway is around 10 0.000 t, and the reduction in the energy consumption accounts for 20 MNOK/year. The use of a natural gas based raw material by substituting partly coal will reduce the CO2 emissions from the production, and especially fossil CO2 emissions. A typical coal used contains around 40% volatiles that will be driven off at the furnace top. Use of the 25% of the new material in the raw material mix by reducing coal from 80 to 55%, will reduce the specific CO2 emission by 0.5 t CO2/t Si, corresponding to a reducti on by around 10%. Taken all Elkem?s production capacity into account, this corresponds to a reduction of fossil CO2 emissions of 50.000 t CO2/year. Industrial implementation of the SiNG results start at the end of the project period, and can be used in Si and FeSi production at the present furnace technology. This differs from other research initiatives using natural gas as reductant on Si/FeSi production where a new process technology has to be developed.