Sulfur Burning Plant (dark and bright sulfur)-
Sulfur is burned and the SO2 gas is converted to SO3 through catalytic contact. SO3 gasses are absorbed by recirculating H2SO4 solution in an absorbing tower.
Ore (pyrite) is roasted. The exit gas is purified, dried and fed into a catalytic converter. SO3 is absorbed on a H2SO4 solution.
Spent Acid plants-
By-products of the organic monomer industry (caprolactam, acrylonitrile) is burned. Exit SO2 is purified, dried, converted and absorbed in H2SO4.
Wet Process (decomposer process)-
The hydrogen sulphite is burned. Exit gas is fed into the converter without being dried.