An improved process for manufacture of sulfuric acid by catalytic oxidation of wet sulfur dioxide gas. Wet conversion gas is contacted with sulfuric acid in a heat recovery stage to effect absorption and generate the heat of absorption. Wet gas having a mole ratio of sulfur trioxide to water vapor of at least 0.95 is introduced into the heat recovery stage at a temperature above the dew point of the gas. Sulfuric acid is introduced into the heat recovery absorption stage at a temperature of at least about 170 DEG C. and a concentration between about 98.5% and about 99.5%. The sulfuric acid stream as discharged from the absorption stage is at a temperature of at least about 190 DEG C. and has a concentration between about 99% and about 100%. The heat of absorption is recovered from the discharge absorption acid stream in useful form by transfer of heat to another fluid in a heat exchanger, the another fluid being heated to a temperature of at least about 140 DEG C. The exit gas stream from the heat recovery stage is contacted with sulfuric acid in a condensing stage for absorption of residual sulfur trioxide and condensation of sulfuric acid vapor. The liquid/gas contact in the condensing stage is carried out before the exit gas is either exhausted from the process or catalytically oxidized to produce additional sulfur trioxide.
