The smelting and production of the silicon metal takes place in Submerged Electric Arc
furnaces, see Figure 6. The furnace is divided into two sections, an upper part above the
smoke hood and a lower part where the actual reaction and the production of the silicon
metal takes place.
The raw materials (yellow) are fed from the day-bins through feeding channels in the smoke
hood and into the furnace. The pre-baked carbon electrodes are placed in the top of the
oven and reach down through the smoke hood into the lower part of the furnace, where the
reaction takes place. In the smoke hood, the off gasses (blue) are collected and transported
to the air treatment units/bag house filters and also heat is conveyed out of the furnace
building.
Regularly, the metal is tapped from the furnace into ladles, re-fined and casted into moulds
in the casting bay. After cooling down, the ingots are pre-crushed and stored in the
intermediate storage within the furnace building. From the intermediate storage the product
is transported to the product crusher bay. After crushing, the product is screened and packed
and stored before transport.
Part of the process involves intermediate compounds such as silicon carbide (SiC(s)) and
silicon monoxide (SiO(g)) gas, which can escape the process and significantly reduce the
yield of the silicon metal. In the furnace shaft a major part of the Silicon monoxide can be
recovered and recycled into the furnace hearth where it participates in the final process. In
the production solid waste is produced only in small amounts, because most of the content
of the raw materials is transformed to Silicon Metal; a certain part moves into the slag and a
considerable part leaves the furnace as silicon monoxide {SiO}, oxidises and precipitates as
Micro Silica captured in the bag house filter. All exhaust from the furnace and the ladle
(refining process) is captured.