The article describes how a sulphuric acid system was designed to use off-gas from a lead smelter to create a steady flow of gas for making sulphuric acid. By absorbing SO2 from the off-gas, the system ensures a consistent concentration of gas for the acid plant. The plant operates in a single-contact process and uses amine solution to reduce emissions of SO2 to safe levels. Key design aspects include how much off-gas is used and the capacity of the amine solution.