Modeling the Electromagnetic Processing of Recycled Silicon Dust

The kerf waste from the sawing of PV silicon wafers is pelletized and then remelted in an induction furnace. The furnace has a square cross-section quartz crucible, surrounded by graphite susceptors and heated by an induction coil that enables directional solidification of the new ingot. Top and bottom ‘pancake’ coils provide additional temperature control. Once melted, silicon becomes electrically conductive and subject to stirring by induction. To recycle the silicon, particulate impurities (due to the sawing, condensed silicon oxides or carbides) need to be removed. Flow control and the electromagnetic Leenov-Kolin force are used to expel particulates, through a novel dual frequency induction scheme. Three-dimensional numerical modeling captures the electromagnetic, fluid-flow and heat-transfer effects in this problem, in a multi-physics finite volume computational framework. Results are presented for typical electromagnetic, velocity and force fields and conclusions are drawn about the expected effectiveness of the electromagnetic separation system which is still under construction.