Exergy based efficiency indicators for the silicon furnace

The production of silicon requires input of carbon and electric power, both high in exergy, in addition to the silicon source (quartz). We report exergy efficiencies of a new furnace for two choices of carbon raw material mixtures and compare this to reported data. From the collected experience for this industry, we propose to evaluate the silicon furnace using a set of two exergy performance indicators: the overall exergy efficiency and the silicon yield exergy indicator, introduced in this work. The new indicator is a measure for the performance of furnace operation. The overall exergy efficiency was 0.30 for both cases of the present furnace. The new silicon yield exergy indicator, together with data from the specific power consumption, favoured the mixture without coal for the present furnace (0.41). Additional exergy introduced as volatiles and through the consumption of electrodes accounted for 8 and 11%, respectively, of the total exergy destruction in the furnace. At 800 °C, the off-gas contained a potential of roughly 25% of the exergy input. This documented the potential to increase the overall exergy efficiency beyond 0.30.