Comparison of Biomass and Coal in the Recovery Process of silicon in an Electric Arc Furnace

Abstract

Silicon recovery of silica ore (${\text{SiO}}_{2}$) has been studied with two types of carbon materials, charcoal as a biomass and coal as a fossil fuel, at elevated temperatures between 1800 and 2000°C in an electric arc furnace. The effects of porosity and electrical resistance of the carbon materials were investigated. To this end, recovery of silicon and ferrosilicon production were tested separately by charcoal and coal, and the products were investigated both qualitatively and quantitatively. A higher electrical resistance of charcoal was found in comparison with coal, with increased efficiency of the furnace and decreased electric energy consumption (per ton of product). The efficiency of the furnace using charcoal and coal was 92.13% and 77.4%, respectively. In addition, the higher porosity of charcoal facilitates the flow of SiO gas through the carbon material leading to a higher reactivity and reducing the electric energy consumption for each ton of FeSi.

Appendix: Calculation of Carbon Material Weight

$$ {\text{X}} = {\text{F}}\frac{{0.4{\text{W}}_{{{\text{SiO}}_{2} }} }}{{\left( {1 - {\text{m}}} \right) \times {\text{fix C}}}} $$

(5)

In Eq. 5, ${\text{X}}$, ${\text{F}}$, ${\text{W}}_{{{\text{SiO}}_{2} }}$, ${\text{m}}$, and fix C are the carbon materials’ weight, weight ratio, quartz rock weight, moisture percentage, and carbon content, respectively.

The amount of ${\text{Si}}$ in the quartz rock in the inlet to the furnace is calculated by Eq. 6:

$$ {\text{Si}}_{\text{inlet}} = {\text{W}}_{{{\text{SiO}}2}} \frac{{{\text{M}}_{\text{Si}} }}{{{\text{M}}_{{{\text{SiO}}_{2} }} }}\left( P \right) $$

(6)

In Eq. 6, ${\text{Si}}_{\text{inlet}}$, ${\text{W}}_{{{\text{SiO}}2}}$, ${\text{M}}_{\text{Si}}$, ${\text{M}}_{{{\text{SiO}}_{2} }}$, and $P$ are the amount of ${\text{Si}}$ in the quartz rock, quartz rock weight, ${\text{Si}}$ molecular weight, ${\text{SiO}}_{2}$ molecular weight, and quartz rock purification percentage, respectively. The value of ${\text{Si}}$ in the melt outlet from the furnace is calculated by Eq. 7 as follows:

$$ {\text{Si}}_{\rm{outlet}} = {\text{W}}_{\rm{melt}} \cdot {\text{p}}^{\prime} $$

(7)

In Eq 7, ${\text{Si}}_{\text{outlet}}$, ${\text{W}}_{\text{melt}}$, and $p^{\prime }$ are the values of ${\text{Si}}$ in the melt outlet from the furnace, the melt weight, and the ${\text{Si}}$ weight percentage in the melt, respectively. Finally, the efficiency of ${\text{Si}}$ recovery ($ef_{Si}$), based on Eqs. 5–7, is calculated as Eq. 4:

$$ ef_{\text{Si}} = \frac{{{\text{Si}}_{\rm{outlet}} }}{{{\text{Si}}_{\rm{inlet}} }}\cdot 100 $$

(8)