Boron removal from silicon with large area reactors – BRESILAR

Solar grade silicon, needed to supply the ever growing photovoltaic market, has to be purified from metallurgical silicon. The classical chemical route for purification has a high energy cost and environmental drawbacks. The alternative metallurgical route has to decrease its production cost to meet with the low market price. This project provides a technology breakthrough compared to existing processes to remove boron and eventually phosphorus, where France has a leading position.

A process will be developed for gas liquid deboration in a special equipment with large interfacial area, increasing strongly the purification rate. This equipment will use chemical reactions between the liquid silicon and reactive gases containing hydrogen an oxygen, well known in our consortium. During the first phase of the project, planned for two years, a small scale configuration will be used to get the reaction rate at laboratory scale, and extrapolate to industrial size. During the second phase, a medium scale configuration will be tested, to solve the technical problems related to upscaling, and to adjust the extrapolation method giving projections for the industrial scale.
The material quality will be evaluated in both phases, with standard chemical analysis methods and with the expertise present in the consortium. To make those analysis available online for a future industrial equipment, a novel analysis method will be developed for liquid silicon, from the adaptation of an existing method used for the moment only on solid samples.
The project includes a cost study of the process when upscaled to industrial size. This extrapolation will be based on the laboratory-scale results and on models developed by the research partners, using the expertise of the industrial partner in the field of equipment manufacturing for high temperature processes.

Two milestones are planned in the project: a mid-term assessment, after 2 years, and a final assessment, after 3,5 years (end of the project). Each milestone will be formalized by a complete report, and be discussed in a meeting where ANR representatives will be invited. In between, the project will be coordinated with regular meetings every six months, where deliverables will be presented and discussed among partners. Other informal communication is easy between partners which are all located within 50km.
The mid-term assesment will examine the results of the small scale experiment, the material it produced, and its extrapolated performance to industrial size. The second phase of the project will be enabled as planned or modified, as a function of those results. The final assesment will examine the results of medium size experiment, online analysis and final extrapolation, and it will validate the roadmap proposed to develop an industrial pilot after the project.
The consortium includes two research institutes (SIMaP and CEA) with scientific and technical knowledge of the purification processes (calibrated models and experiments available), and of the material quality (various characterization methods available). The industrial partner (ECM Greentech) is an equipment manufacturer interested in the industrialisation of purification facilities, mainly for exportation.

At the end of the project, a development program will be available to have an industrial pilot within two years. The lab-scale experiment will be available for further R&D to support this technological roadmap. The online measurement of liquid silicon purity will be available for different use in the metallurgical purification route to provide solar grade silicon.