Abstract: In a system using the double absorption process for sulphuric acid manufacture, a single acid circulation system and a single cooler are employed. Acid from the exit of the air drying tower is circulated to and flows through the final absorber where it absorbs the inlet SO.sub.3 gas before joining with the acid from the intermediate absorber. The mixed stream is then cooled and split between the drying tower and the intermediate absorber. The circulation arrangement reduces the cooling to one relatively high temperature location, eliminates the transfer of SO.sub.2 to the effluent gas from acid in the normal single system, and simplifies acid strength and level control.