Contact sulfuric acid process employing double conversion/double absorption

Claim 1

The process for making sulfuric acid by catalytic oxidation of sulfur dioxide from a cold sulfur dioxide-containing gas stream from a wet gas purification plant involving the steps of: (a) dividing said cold gas stream into a first and a second stream, said second stream comprising from about 1 to about 30 percent by volume of the total gas stream; (b) preheating the first gas stream to the kindling temperature of the catalyst; (c) passing the preheated first gas stream through a primary contact section containing catalyst to effect oxidation of part of the sulfur dioxide to sulfur trioxide; (d) cooling the gas stream from the primary contact section to temperature between about 400° and about 550° F; (e) contacting the gas stream so cooled with sulfuric acid in an intermediate absorption section to effect absorption of sulfur trioxide therefrom; (f) combining the gas stream from the intermediate absorption section with said second gas stream obtained in step a), above, and preheating the combined gas stream to the kindling temperature of the catalyst by indirect heat exchange with hot gases from step g), below, augmented by indirect heat exchange with an external heat source, if necessary; (g) passing the preheated combined gas stream through a secondary contact section containing catalyst to effect oxidation of sulfur dioxide contained therein to sulfur trioxide; (h) cooling the gas stream from the secondary contact section to temperature between about 300° and about 450° F by indirect heat exchange with the gas stream to be introduced into the secondary contact section; followed by (i) contacting the cooled gas stream with sulfuric acid to effect absorption of sulfur trioxide therefrom.