Silicon production with no CO₂ emission, by closing the furnace.
SiNoCO₂ is a R&D project that will research methods to develop a significantly more energy-efficient concept for producing silicon alloys with no direct CO₂ emissions from the production furnaces.
Partners: NTNU - Department of Material Science and Engineering; Sintef Materials and Chemistry; Teknova AS.
Funding period: 2017-2020
Main goal: to develop a significantly more energy-efficient concept for production of silicon alloys with no direct CO₂ emissions.
Very simplified, the goal is to "close the silicon furnace". As a result, the off-gas from the furnace will mainly contain CO, which can be further exploited for energy production or chemical manufacturing such as hydrogen production.
The new production concept could also be an important step on the road to CO₂-negative silicon production, because it will be possible to use carbon capture and storage (CCS) in addition to the ongoing work to replace coal from fossil sources with charcoal. CCS is said to be key to reach targets defined in the Paris Agreement (2015) and has been pointed to as part of the solution in the process industry road map from 2016 (in Norwegian).
Furthermore, the SiNoCO₂ project will examine whether it is possible to operate a furnace at 100% silicon yield, so that all silicon in the quartz raw materials is tapped as liquid silicon from the furnace, with zero emission containing from gas from the furnace top.
Obstacles to overcome
Two practical challenges need to be solved. Firstly, to close the furnaces the material flow, the energy distribution and the chemical reactions inside the furnace must be controlled. A stoking free process or automatic stocking must be developed. Secondly, closed furnaces must be operated without direct observation. A monitoring technology for the furnaces is a solution.
If the obstacles are solved the gains will be large. There is a potential form 40% reduction in energy consumptions per tonne of silicon. The NOₓ emissions from the furnace will be reduced by more than 90%. Costs for removing sulphur and other elements will also be reduced. The operational cost of closed furnaces is expected to be 60-70% of the cost level today.
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.
A great challenge
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 inside 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 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?
Cooperation and partnership
The projects is divided into three work packages:
- 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.
- Investigation on 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.
- Industrial verification of the R&D results by developing an integrated process design for FeSi/Si alloy production utilizing the CO gas, maximizing the overall energy and material efficiency and reducing the off gas emissions.
Elkem Technology is the project owner and manager of SiNoCO₂. SINTEF, NTNU and Teknova AS are Norwegian research partners in the project. Both Elkem Foundry Products and Elkem Silicon Materials represent future users of the technology.
SiNoCO₂ is financed by the EnergiX program by The Research Council of Norway, and the funding period is from 2017-2020.