Life cycle assessment of the conventional and solar thermal production of zinc and synthesis gas

The current industrial productions of zinc and synthesis gas are characterized by their high energy consumption and their concomitant environmental pollution. Emissions of greenhouse gases (GHG) could be reduced substantially by combining both productions and by replacing fossil fuels with concentrated solar energy as the source of high-temperature process heat. The extent of such a GHG mitigation has been quantified by conducting a Life Cycle Assessment on the solar- and fossil-fuel-based processes. Total GHG emissions for the conventional zinc production are 3.14 CO2-eq per kg primary zinc (99.995% purity), of which 64% are derived from the electricity consumption in the electrolytic step. Total GHG emissions for the conventional syngas production are 1.04 CO2-eq per kg syngas (molar ratio H2/CO=2), of which 84% are derived from the combustion of fossil fuels in the endothermic steam-reforming step. Total emissions for the solar combined process are 1.51 CO2-eq per 1 kg zinc and 0.527 kg syngas, of which 78% are derived from the pre-/post-processing of reactants and products of the solar reactor, and 16% are derived from their transportation to/from the solar site. However, CO2-eq emissions derived from the solar processing step and its infrastructure are negligible.