A commercial-scale flow-reversed SO, converter with two inter-stage heat exchangers has been studied based on the author's practices in a lead smelter. A control strategy with two control loops of cooling and cycling durations, and an special device ensuring the outlet temperature stability have been proposed and operated smoothly. Normally, the SO, final conversion is higher then 92%, and the maximum temperature is between 530 and 560 degrees C as the SO2 composition fluctuates within 1.0 and 4.5%(vol). Problems related to the commercialization of unsteady-state SO2 converter are also discussed.