Concentrated sulphuric acid is manufactured in a process with two contact stages in the presence of steam

A process for the manuf. of conc. H2SO4 by the catalytic conversion of SO2 to SO3 in the presence of water vapour takes place in 2 contact stages. In the 1st stage, the reaction gas used contains part of the required H2O such that the gas leaving the 1st stage has a mole ratio of H2O/SO3 of 0.9-1.1. This gas is cooled by indirect heat exchange with the gas being fed into the 2nd stage. The gas is cooled in a steam generation unit so that the H2SO4 vapour formed condenses. The generator consists of a superheater, a vaporiser and an economiser. The temp. of the gas leaving the steam generator is < 160 deg C. The steam is produced in the generator at 5 to 30 bar. The remaining gas is fed into the 2nd stage after bringing it to working temp.