Gas Composition Below Equilibrium Curve

A 1 catalyst bed oxidizes less than 80% of its feed SO2 to SO3. This percentage is increased by passing its exit gas through a series of gas cooling/catalytic oxidation steps. 

Gas cooling between catalyst beds is done in water-to-steam boilers, superheaters, economizers and gas-to-gas heat exchangers. Gas composition doesn t change in these cooling devices because they don t contain catalyst. 

Gas cooling between 1 and 2 catalyst beds is represented graphically by a horizontal line at  

12volume% SO2, 13.2volume% O2, 74.8 volume% N2 first catalyst bed feed gas. 

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