Because of the tight pollution control of $SO_2$ emission, sulfuric acid manufacturers have been interested in the operation with the highest possible conversion efficiency. In this work, the design criteria and operating conditions of the catalytic converter were investigated for maximum conversion efficiency and minimum $SO_2$ emission by parametric analysis and process optimization for the existing acid plants. The Double Converter/Double Absorber(DC/DA) process was investigated by varying $SO_2$ compositions of feed gas, pressures and temperatures of layers of the converter and the depth of the catalyst beds. In order to evaluate the process, a computer simulator for sulfuric acid plants has been developed. The results by process optimization could be used for the converter design and operating conditions with highest conversion efficiency.