The co-production of Zn and synthesis gas by the combined reduction of ZnO and reforming of CH4 has been performed using a vortex-flow chemical reactor in a high-flux solar furnace. The reactor operating temperature ranged between 1221 and 1481 K for an 2 input solar power of 2.3 to 4.6 kW and mean solar flux intensities of 810 to 1609 kW/m(2). The performance of the reactor was determined by conducting a complete mass and energy balance for the chemical process. The chemical conversion ranged between 83-100 percent. The thermal efficiency, defined as the portion of input solar power absorbed as sensible and process heat, was in the range 11-28 percent. The exergy efficiency for the closed cycle, defined as the ratio of the maximum amount of work that the products leaving the reactor could produce if were re-combined to the input solar power, was in the range 0.3-3.1 percent. Major sources of energy loss are re-radiation heat transfer through the reactor aperture, conduction heat transfer through the reactor walls, and the quenching of the reaction products.