THERMODYNAMIC ANALYSIS OF THE COPRODUCTION OF ZINC AND SYNTHESIS GAS-USING SOLAR PROCESS HEAT

We present a solar thermochemical process that combines the reduction of zinc oxide with the reforming of natural gas (NG) for the co-produc tion of zinc and syngas. The overall reaction may be represented by Zn O+CH4 = Zn+2H(2)+CO. The maximum possible overall efficiency is assess ed for an ideal, closed cyclic system that recycles all materials and also for a more technically-feasible open system that allows for mater ial flow into and out of the system. Assuming that the equilibrium che mical composition is obtained in a blackbody solar reactor operated at 1250 K, 1 atm, and with a solar power-flux concentration of 2000, clo sed-cycle efficiencies vary between 40 and 65%, depending on recovery of the product sensible heat. Under the same baseline conditions, open -cycle efficiencies vary between 36 and 50%, depending on whether a Zn /O-2 or an H-2/O-2 fuel cell is employed. Compared to the HHV of metha ne for generating electricity, the proposed solar open-cycle process r eleases half as much CO2 to the atmosphere. The process modelling desc ribed in this paper establishes a base for evaluating and comparing di fferent solar thermochemical processes.