SiNoCO2 - Silicon production with no CO2 emissions

The project name SiNoCO2 actually describes the goal of the project. We will do research on possible methods for producing silicon alloys with no direct CO2 emissions from the production furnaces. Very simplified, this means that we are going to "close the silicon furnace". We will then get an off gas from the furnace that mainly contains CO, which can be further exploited for energy production or raw material for chemical manufacturing. The biggest challenge for "closing the furnace" is to find out how we can control the material flow, the energy distribution and the chemical reactions in the furnace. We need to develop a "stoking free" process, alternatively a form of automatic stoking of the furnace, and in addition, we need to operate the furnace without looking the possibility of direct observations of the furnace surface. We will also examine whether it is possible to operate a furnace at 100% silicon yield. By this, we mean that all silicon in the quartz raw materials is tapped as liquid silicon from the furnace, and that we do not have any emission of SiO gas from the furnace top. What are the obstacles preventing us from operating at 100% silicon yield? Can we modify the furnace design in a way that makes this possible? The SiNoCO2 project will go for 5 years and end in December 2021. Elkem Technology is the project owner and project manager. SINTEF Industry, NTNU and NORCE (former Teknova) are research partners in the project, and the project includes a PhD candidate and several MSc candidates. The Elkem division producing silicon alloys, Elkem Silicon Products, is industry partner in the project. SINTEF has studied what happens with SiO gas that leaves the furnace when there is no available oxygen to burn SiO to SiO2. The current testing equipment has shown to be inappropriate for this. The trials were planned to be conducted when a new two-zone oven was installed at Sintef in 2019. However, the installation of the two-zone furnace has been delayed several times and is still not operating at the end of 2021, so that we cannot run tests in it in this project. The postponement of the laboratory tests enabled a larger measurement campaign to be carried out on an industrial ferrosilicon smelting furnace in Elkem in November 2018. The gas and temperature conditions differ on a silicon furnace, so a similar measurement was done on a silicon furnace in October 2019. Chemical composition of gases in the upper part of the furnace and in the off-gas system from the furnace hood was measured. The measurement results have given new insight about how these conditions varies in a smelting furnace. It has provided important, and necessary, information to adapt the process models developed in the project. A third campaign was planned to be carried out in November 2020 but was postponed to June 2021. The gas in Elkem's furnaces is a mixture of SiO and CO. The gas partly condenses on its way to the top and forms solids, called SiO condensates. The PhD candidate at NTNU started his work in July 2017 and investigated the formation of various SiO condensates. It is important to understand these mechanisms that prevent descend of the materials in the furnace. The PhD student finishing his work in December 2020 and defended his degree in March 2021. Atomistic modelling has also been carried out at Sintef of the various chemical reactions between the various gas components in the furnace. NORCE has developed a model for the understanding of crust formation in the furnace (hard layer with SiO condensate). Analyses of data from the measurement campaign at the furnace in November 2018 showed that a better understanding is required about the conditions in the upper part of the "charge" in the furnace, and that the physical processes in this region should be modelled. The project has therefore prioritized to develop a model for this part of the furnace. Measurements have been made on the gas composition, especially with a focus on CO2 concentration, on several of Elkem's furnaces. This is done to verify models and hence the potential for the use of the off gas. This work has continued in 2020. These results work have been transferred to a feasibility study Elkem is conducting, with support from Gassnova, to look at possible technologies and investment and operating costs for CO2 capture at Elkem's smelters. The project financed together with Gassnova, FME HighEff and SFI Metal production a large test campaign at NTNU on off gas recirculation from a pilot silicon furnace. NORCE and Elkem have completed a technical-economic calculation model to study various possibilities for using the exhaust gas from the furnace. We are now using the model to evaluate different cases.

Prosjektet konkluderte med at det ikke vil være mulig å lukke silisiumprosessen med dagens prosessteknologi og anbefalte at avgassen resirkuleres slik at CO2 konsentrasjonen økes i avgassen med påfølgende karbonfangst. Prosjektet målte avgass-sammensetning på alle Elkems smelteovner og dokumenterte nivåer og variasjoner i CO2. Elkem har tatt dette videre i et prosjekt, støttet av Gassnova CLIMIT, i 2020-21 med mulighetsstudie av karbonfangst og lagring på Elkems smelteverk. Dette prosjektet videreføres med pilottesting av karbonfangst på en av Elkems smelteovner. Målekampanjene for temperatur og gass-sammensetning som er gjennomført ved industrielle ovner har gitt helt ny kunnskap om hvordan temperaturforholdene er i øvre deler av silisium og ferrosilisiumovner. Prosjekt har bidratt i å etablere ny kunnskap som muliggjør at Elkem raskere kan implementere karbonfangst på sine smelteovner, noe som er viktig for Norges reduksjon i CO2 utslipp.

The SiNoCO2 project will develop a new concept for Si alloy production by "closing" the furnace hood, ensuring that no air comes into the process. This will enable direct use of CO from the process off gas, no oxidation of carbon raw materials at the furnace top, and more efficient energy recovery due to the reduced flow rate of off gas. Moreover, the SiNoCO2 project will also exploit the possibility of operating Si alloy furnaces at 100% Si yield, and evaluate alternative methods for production of Si alloys. The projects is divided into three work packages: - [H1] Fundamental study of how the present furnace technology can be closed by solving process obstacles in the production process and controlling the novel off gas conditions. - [H2] Fundamental study of how 100% Si yield can be achieved with the present production concept by application of engineered raw materials and minor process modifications. A PhD study will be part of this work. - [H3] Industrial verification of closed Si alloy furnace concept utilizing the CO gas, maximizing the overall energy and material efficiency and reducing the off gas emissions. The SiNoCO2 project is a collaborative project where Elkem AS, Technology is the project owner, and Elkem AS divisions Silicon Materials and Foundry Products are industry partners. The research-performing partners are NTNU - Department of Material Science and Engineering, Sintef Materials and Chemistry and Teknova. One PhD study and one or more MSc work will be conducted as part of the project. NTNU - Department of Material Science and Engineering will be responsible for completion of PhD studies.