Patent ID: 7361326

Claim:
Process of producing sulfuric acid from feed gases containing 0.1-30% SO 2 comprising the steps of: (a) passing the feed gas to a first catalytic conversion step in which SO 2 is oxidized to SO 3 over one or more catalyst beds, (b) cooling the SO 3 -containing gas from said first contacting step by passing said gas to an intermediate condensing stage withdrawing a gas containing unconverted SO 2 and unabsorbed SO 3 and withdrawing a product stream of concentrated sulfuric acid, (c) reheating said gas containing unconverted SO 2 and unabsorbed SO 3 , (d) passing the gas from step (c) to a second catalytic conversion step, in which unconverted SO 2 is oxidized to SO 3 over one or more catalyst beds, (e) cooling the gas from step (d) to a temperature of 0 to 100° C. above the acid dew point of said gas, (f) passing the gas from step (e) with a molar ratio of H 2 O to SO 3 of at least 1.05 calculated under the assumption that SO 3 is not hydrated to H 2 SO 4 and acid dew point of below about 240° C. to a final wet condensing stage, in which the remaining sulfuric acid is condensed by cooling of said gas by indirect or direct heat exchange with a cooling medium, (g) providing in the gas, prior to conducting step (f), a content of 10 10 to 10 13 solid particles per Nm 3 per vol % SO 3 calculated under the assumption that SO 3 is not hydrated to H 2 SO 4 , and (h) withdrawing from the final wet condensing stage of step (f) a stream of 70-98 wt % sulfuric acid.