20.10.2018 Views

knjiga solarna energija dobra

Create successful ePaper yourself

Turn your PDF publications into a flip-book with our unique Google optimized e-Paper software.

164 SOLAR GRADE SILICON FEEDSTOCK<br />

the degree of refining is determined by distribution equilibria (5.20) to (5.23), where the<br />

(parentheses) refer to components dissolved in a slag phase and the underscored symbols<br />

refer to dissolved elements in liquid silicon:<br />

4Al + 3(SiO 2 ) = 3Si(l) + 2(Al 2 O 3 ) (5.20)<br />

2Ca + SiO 2 = Si(l) + 2(CaO) (5.21)<br />

2Mg + SiO 2 = Si(l) + 2(MgO) (5.22)<br />

S(l) + O 2 = (SiO 2 ) (5.23)<br />

Theoretically it is possible to remove Al and Ca to very low levels, but in practice this<br />

is prevented by the large heat losses occurring during this operation. Temperature drops<br />

to 1700 to 1500 ◦ C, and to avoid freezing of the melt, some of the silica needed for slag<br />

Raw material<br />

C SiO 2<br />

Consumable<br />

electrodes<br />

Cleaned gas<br />

Electric energy<br />

Filter<br />

Charge material<br />

Liquid metal<br />

Refining<br />

Crater<br />

Recovered<br />

energy<br />

Silica<br />

Solidification<br />

Sizing<br />

Crushing<br />

Silicon<br />

(a)<br />

Figure 5.1 (a) and (b) Schematic representation of a furnace for production of metallurgical<br />

grade silicon. Reproduced from Schei A, Tuset J, Tveit H, Production of High Silicon Alloys, Tapir<br />

forlag, Trondheim (1998) with permission by Haluard Tueit

Hooray! Your file is uploaded and ready to be published.

Saved successfully!

Ooh no, something went wrong!