Assumes ten percent of S reaches SRU via SWS.  Actuals range from 8% to 40%.

Solubility of H2S in water is low, but reaction with ammonia forms highly soluble NH4HS.  Therefore, the mol ratio of N to S in sour water is about 1.

Best ammonia destruction in Claus is achieved under oxidizing conditions, requiring that the H2S in SWSG fed to a Claus train not exceed 1/3 of the total H2S fed.

Variation in  the rate or composition of SWSG to Claus challenges control of the air rate.

When O2 is deficient, ammonia salts and coke plug the catalyst. 

When O2 is in excess, the SO2 formed exceeds stoichiometric demand, increasing cost of chemical reduction in the TGT and sometimes breaking through into the quench and amine scrubbers.  Increases formation of SO3.

Calculate Claus capacity in terms of equivalent AAG S rate.  Compared to S fed as AAG, S as SWSG produces about 2.5 times the gas rate in Claus.   Recycle H2S from TGT produces about 1.6 times as much gas because it contains about as much CO2 as H2S.  AAG eq = 126 tpd