Energy and exergy analysis of the silicon production process

• The exergetic efficiency for an industrial silicon production process when silicon is the only product was estimated to 0.33.
• With additional power production from thermal energy in the off-gas we estimated the exergetic efficiency to 0.41.
• The theoretical silicon production process is established as the reference case.
• Exergy lost with the off-gas and exergy destructed due to combustion account for roughly 75% of the total losses.
• With utilization of the thermal exergy in the off-gas at a temperature of 800 °C the exergetic efficiency was 0.71.

We used energy and exergy analysis to evaluate two industrial and one ideal (theoretical) production process for silicon. The industrial processes were considered in the absence and presence of power production from waste heat in the off-gas. The theoretical process, with pure reactants and no side-reactions, was used to provide a more realistic upper limit of performance for the others. The energy analysis documented the large thermal energy source in the off-gas system, while the exergy analysis documented the potential for efficiency improvement. We found an exergetic efficiency equal to 0.33 ± 0.02 for the process without power production. The value increased to 0.41 ± 0.03 when waste heat was utilized. For the ideal process, we found an exergetic efficiency of 0.51. Utilization of thermal exergy in an off-gas of 800 °C increased this exergetic efficiency to 0.71. Exergy destructed due to combustion of by-product gases and exergy lost with the furnace off-gas were the largest contributors to the thermodynamic inefficiency of all processes.