## 2 Materials and Methods
Therefore, we do not provide a separate description for them here. There were proposals to use a non-standard carbonaceous reducing agent called Rexyl, which is described in the literature [21]. However, to ensure the purity of the experiment, it was decided to postpone the Rexyl test for the future and not to combine two tests in one period. To achieve balanced smelting of the silicon metal, we used the approach we described previously [10]. However, since balanced smelting is the basis of our know-how for working with through hole electrodes, we will briefly repeat it again. We set and maintained active power during the entire testing period (furnace load) 19.5 MW. We expected that the specific power consumption would be 12.5 MWh per 1 ton of silicon metal in the form of a solid product after tapping, casting and crystallization in the mold. This would mean that the furnace's productivity would be 19.5/12.5 = 1.56 t/h or the need for quartz \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Diameter, mm** & **Brand S** & **Brand G** \\ \cline{2-4}  & **Permissible Current Strength, A** & **Current Density, (A/cm\({}^{2}\))** & **Permissible Current Strength, A** & **Current Density, (A/cm\({}^{2}\))** \\ \hline
1272 & 73,600 & 5.8 & 85,100 & 6.7 \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Electrical characteristics of carbon electrodes from Hebei Orient Carbon Co., Ltd.  
Figure 5: Carbon electrodes: (**a**) El6 Group, (**b**) Hebei Orient Carbon Co., Ltd. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Type** & **Brand S** & **Brand G** \\ \hline Apparent density, no less than, g/cm\({}^{3}\) & 1.58 & 1.58 \\ \hline Specific electrical resistance, no more than, \(\mu\)Ohm & 35 & 30 \\ \hline Ash content, no more than, \% & 4.5 & 4.0 \\ \hline Bending strength, no less than, MPa & 6.5 & 6.5 \\ \hline Thermal expansion coefficient, (t 20-520 \({}^{\circ}\)C), no more than, \(\times 10^{-6}\) K\({}^{-1}\) at 20 \({}^{\circ}\)C & 4.5 & 4.0 \\ \hline \hline \end{tabular}
\end{table} 
Table 7: Technical characteristics of carbon electrodes from Hebei Orient Carbon Co., Ltd.  
1.56 \(\times\) 60/28 = 3.3428 t/h, subject to the 100% extraction of silicon into the finished product. Then, we had to decide for ourselves what kind of silicon recovery we would focus on. Considering that, at \"Tau-Ken Temir\" LLP, silicon recovery is very poor, we started the first week of testing with a conservative level: 75%. Thus, the loading intensity for quartz should have been 3.3428/0.75 = 4.457 t/h. In the following weeks of testing, we strived to consistently reduce assumptions of the specific power consumption and increase the silicon recovery in the finished product. Unlike the first experience of carrying out balanced smelting in 2017, we abandoned the concept of excess charge because it strongly depends on the values of specific power consumption and silicon recovery conventionally accepted in calculations. Instead, we used absolute values of the hourly consumption of quartz for smelting. Testing began with the gradual replacement of graphite electrodes with carbon ones. At a certain point, the expansion of electrode columns began with carbon electrodes instead of graphite ones. The total length of the electrode column was about 22 m. With a length of one piece of electrode of 2.7 m, the number of pieces per column is 22/2.7 = 8.1 pcs. The weight of one 2.7-m-long piece of electrode was 4.9 tons (1.814 t/m). Thus, the weight of one electrode column was 4.9 \(\times\) 8 = 39.2 tons (three columns 39.2 \(\times\) 3 = 117.6 tons). The specific consumption of the electrode was about 0.1 t/t of silicon metal. With a productivity of 1.56 t/h (37.44 t/day) of silicon metal, the daily consumption of the electrode would be 37.44 \(\times\) 0.1 = 37.44 tons. The gradual, natural replacement of graphite electrodes with carbon electrodes took 117.6/3.744 = 31.4 days. Accordingly, the available supply of 110 tons of carbon electrodes was enough to test within 4 weeks.