Alternatives to gas recycle

This common method is used to treat high SO2 concentrafitMi feed gas produced by oxygen-enriched metallurgical processes (Table 4-1). Dilution air lowers the feed gas SO2 concentration and provides oxygen required for efficient catalytic SO2 oxidation. 

Item Unit From gas cleaning plant Dilution air To drying tower To first catalyst bed 

Air is filtered to remove dust and is drawn into the process gas ahead of the drying tower (Chapter 6). Table 27.3 provides an example where dilution air increases the total gas flow to the acid plant by 140%. 

Dilution air addition increases equipment size and increases the energy required to move gas through the acid plant. Nearly 30% less dilution air is required if the feed gas entering the first catalyst bed is at 16 volume% SO2 instead of 13 volume%. This is why acid plant designers continue to look for ways to treat high SO2 concentration feed gas. 

Feed gases with up to 18 volume% SO2 have been treated in an acid plant using a preconverter (PuriceUi et al., 1998). A portion of the high SO2 concentration feed gas is diluted with dry air and sent to the preconverter (Fig. 27.9) where a portion of the SO2 is oxidized to SO3. SOa-bearing gas leaves the preconverter and is combined with the remaining portion of feed gas entering the first catalyst bed. This decreases the first catalyst bed exit gas temperature. 

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Alternatives to gas recycle include air dilution or preconverters. The new BAYQIK preconverter is a quasi-isothermal reactor. 

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